pgstat: store statistics in shared memory.
authorAndres Freund <[email protected]>
Thu, 7 Apr 2022 04:29:46 +0000 (21:29 -0700)
committerAndres Freund <[email protected]>
Thu, 7 Apr 2022 04:29:46 +0000 (21:29 -0700)
Previously the statistics collector received statistics updates via UDP and
shared statistics data by writing them out to temporary files regularly. These
files can reach tens of megabytes and are written out up to twice a
second. This has repeatedly prevented us from adding additional useful
statistics.

Now statistics are stored in shared memory. Statistics for variable-numbered
objects are stored in a dshash hashtable (backed by dynamic shared
memory). Fixed-numbered stats are stored in plain shared memory.

The header for pgstat.c contains an overview of the architecture.

The stats collector is not needed anymore, remove it.

By utilizing the transactional statistics drop infrastructure introduced in a
prior commit statistics entries cannot "leak" anymore. Previously leaked
statistics were dropped by pgstat_vacuum_stat(), called from [auto-]vacuum. On
systems with many small relations pgstat_vacuum_stat() could be quite
expensive.

Now that replicas drop statistics entries for dropped objects, it is not
necessary anymore to reset stats when starting from a cleanly shut down
replica.

Subsequent commits will perform some further code cleanup, adapt docs and add
tests.

Bumps PGSTAT_FILE_FORMAT_ID.

Author: Kyotaro Horiguchi <[email protected]>
Author: Andres Freund <[email protected]>
Author: Melanie Plageman <[email protected]>
Reviewed-By: Andres Freund <[email protected]>
Reviewed-By: Thomas Munro <[email protected]>
Reviewed-By: Justin Pryzby <[email protected]>
Reviewed-By: "David G. Johnston" <[email protected]>
Reviewed-By: Tomas Vondra <[email protected]> (in a much earlier version)
Reviewed-By: Arthur Zakirov <[email protected]> (in a much earlier version)
Reviewed-By: Antonin Houska <[email protected]> (in a much earlier version)
Discussion: https://postgr.es/m/20220303021600[email protected]
Discussion: https://postgr.es/m/20220308205351[email protected]
Discussion: https://postgr.es/m/20210319235115[email protected]

50 files changed:
doc/src/sgml/monitoring.sgml
src/backend/access/transam/xlog.c
src/backend/commands/vacuum.c
src/backend/commands/vacuumparallel.c
src/backend/postmaster/autovacuum.c
src/backend/postmaster/checkpointer.c
src/backend/postmaster/interrupt.c
src/backend/postmaster/pgstat.c
src/backend/postmaster/postmaster.c
src/backend/replication/logical/logical.c
src/backend/replication/logical/tablesync.c
src/backend/replication/logical/worker.c
src/backend/replication/slot.c
src/backend/storage/buffer/bufmgr.c
src/backend/storage/ipc/ipci.c
src/backend/storage/lmgr/lwlock.c
src/backend/tcop/postgres.c
src/backend/utils/activity/Makefile
src/backend/utils/activity/pgstat_archiver.c
src/backend/utils/activity/pgstat_bgwriter.c
src/backend/utils/activity/pgstat_checkpointer.c
src/backend/utils/activity/pgstat_database.c
src/backend/utils/activity/pgstat_function.c
src/backend/utils/activity/pgstat_relation.c
src/backend/utils/activity/pgstat_replslot.c
src/backend/utils/activity/pgstat_shmem.c [new file with mode: 0644]
src/backend/utils/activity/pgstat_slru.c
src/backend/utils/activity/pgstat_subscription.c
src/backend/utils/activity/pgstat_wal.c
src/backend/utils/activity/pgstat_xact.c
src/backend/utils/activity/wait_event.c
src/backend/utils/adt/pgstatfuncs.c
src/backend/utils/cache/relcache.c
src/backend/utils/init/globals.c
src/backend/utils/init/miscinit.c
src/backend/utils/init/postinit.c
src/backend/utils/misc/guc.c
src/backend/utils/misc/postgresql.conf.sample
src/include/miscadmin.h
src/include/pgstat.h
src/include/storage/lwlock.h
src/include/utils/pgstat_internal.h
src/include/utils/rel.h
src/include/utils/timeout.h
src/include/utils/wait_event.h
src/test/modules/worker_spi/worker_spi.c
src/test/regress/expected/stats.out
src/test/regress/sql/stats.sql
src/tools/pgindent/typedefs.list
src/tools/valgrind.supp

index 487331c115372ade775fd31b23d47bd7c9c3dd7f..24924647b5fc5c000502d8dbecf391ebd758b2e0 100644 (file)
@@ -1110,10 +1110,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry><literal>LogicalLauncherMain</literal></entry>
       <entry>Waiting in main loop of logical replication launcher process.</entry>
      </row>
-     <row>
-      <entry><literal>PgStatMain</literal></entry>
-      <entry>Waiting in main loop of statistics collector process.</entry>
-     </row>
      <row>
       <entry><literal>RecoveryWalStream</literal></entry>
       <entry>Waiting in main loop of startup process for WAL to arrive, during
@@ -2115,6 +2111,18 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry>Waiting to access the list of predicate locks held by
        serializable transactions.</entry>
      </row>
+     <row>
+      <entry><literal>PgStatsDSA</literal></entry>
+      <entry>Waiting for stats dynamic shared memory allocator access</entry>
+     </row>
+     <row>
+      <entry><literal>PgStatsHash</literal></entry>
+      <entry>Waiting for stats shared memory hash table access</entry>
+     </row>
+     <row>
+      <entry><literal>PgStatsData</literal></entry>
+      <entry>Waiting for shared memory stats data access</entry>
+     </row>
      <row>
       <entry><literal>SerializableXactHash</literal></entry>
       <entry>Waiting to read or update information about serializable
@@ -5142,7 +5150,8 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
         <returnvalue>timestamp with time zone</returnvalue>
        </para>
        <para>
-        Returns the timestamp of the current statistics snapshot.
+        Returns the timestamp of the current statistics snapshot, or NULL if
+        no statistics snapshot has been taken.
        </para></entry>
       </row>
 
index 8ae0a0ba537a381d59ddec5d0b20c75e5f587e29..c076e48445d054b716a50f3aeb4bd8e3056b93f5 100644 (file)
@@ -1842,7 +1842,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
                                        WriteRqst.Flush = 0;
                                        XLogWrite(WriteRqst, tli, false);
                                        LWLockRelease(WALWriteLock);
-                                       WalStats.m_wal_buffers_full++;
+                                       PendingWalStats.wal_buffers_full++;
                                        TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
                                }
                                /* Re-acquire WALBufMappingLock and retry */
@@ -2200,10 +2200,10 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 
                                        INSTR_TIME_SET_CURRENT(duration);
                                        INSTR_TIME_SUBTRACT(duration, start);
-                                       WalStats.m_wal_write_time += INSTR_TIME_GET_MICROSEC(duration);
+                                       PendingWalStats.wal_write_time += INSTR_TIME_GET_MICROSEC(duration);
                                }
 
-                               WalStats.m_wal_write++;
+                               PendingWalStats.wal_write++;
 
                                if (written <= 0)
                                {
@@ -4877,6 +4877,7 @@ StartupXLOG(void)
        XLogCtlInsert *Insert;
        CheckPoint      checkPoint;
        bool            wasShutdown;
+       bool            didCrash;
        bool            haveTblspcMap;
        bool            haveBackupLabel;
        XLogRecPtr      EndOfLog;
@@ -4994,7 +4995,10 @@ StartupXLOG(void)
        {
                RemoveTempXlogFiles();
                SyncDataDirectory();
+               didCrash = true;
        }
+       else
+               didCrash = false;
 
        /*
         * Prepare for WAL recovery if needed.
@@ -5106,6 +5110,22 @@ StartupXLOG(void)
         */
        restoreTwoPhaseData();
 
+       /*
+        * When starting with crash recovery, reset pgstat data - it might not be
+        * valid. Otherwise restore pgstat data. It's safe to do this here,
+        * because postmaster will not yet have started any other processes.
+        *
+        * NB: Restoring replication slot stats relies on slot state to have
+        * already been restored from disk.
+        *
+        * TODO: With a bit of extra work we could just start with a pgstat file
+        * associated with the checkpoint redo location we're starting from.
+        */
+       if (didCrash)
+               pgstat_discard_stats();
+       else
+               pgstat_restore_stats();
+
        lastFullPageWrites = checkPoint.fullPageWrites;
 
        RedoRecPtr = XLogCtl->RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;
@@ -5180,11 +5200,6 @@ StartupXLOG(void)
                        LocalMinRecoveryPointTLI = 0;
                }
 
-               /*
-                * Reset pgstat data, because it may be invalid after recovery.
-                */
-               pgstat_reset_all();
-
                /* Check that the GUCs used to generate the WAL allow recovery */
                CheckRequiredParameterValues();
 
@@ -6081,8 +6096,8 @@ LogCheckpointEnd(bool restartpoint)
                                                                                                 CheckpointStats.ckpt_sync_end_t);
 
        /* Accumulate checkpoint timing summary data, in milliseconds. */
-       PendingCheckpointerStats.m_checkpoint_write_time += write_msecs;
-       PendingCheckpointerStats.m_checkpoint_sync_time += sync_msecs;
+       PendingCheckpointerStats.checkpoint_write_time += write_msecs;
+       PendingCheckpointerStats.checkpoint_sync_time += sync_msecs;
 
        /*
         * All of the published timing statistics are accounted for.  Only
@@ -8009,10 +8024,10 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 
                INSTR_TIME_SET_CURRENT(duration);
                INSTR_TIME_SUBTRACT(duration, start);
-               WalStats.m_wal_sync_time += INSTR_TIME_GET_MICROSEC(duration);
+               PendingWalStats.wal_sync_time += INSTR_TIME_GET_MICROSEC(duration);
        }
 
-       WalStats.m_wal_sync++;
+       PendingWalStats.wal_sync++;
 }
 
 /*
index 04dbbe5530af595e69f8f72d4b326f520b92b77e..e0fc7e8d7949c315da4c3bfa65210652d5e418f0 100644 (file)
@@ -351,13 +351,6 @@ vacuum(List *relations, VacuumParams *params,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("PROCESS_TOAST required with VACUUM FULL")));
 
-       /*
-        * Send info about dead objects to the cumulative stats system, unless
-        * we are in autovacuum --- autovacuum.c does this for itself.
-        */
-       if ((params->options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess())
-               pgstat_vacuum_stat();
-
        /*
         * Create special memory context for cross-transaction storage.
         *
index 974a29e7a968086da4ecf574c701125f59991f02..6b4f742578e059ce05f2da54d8ba4d2c454f8c0c 100644 (file)
@@ -28,6 +28,7 @@
 
 #include "access/amapi.h"
 #include "access/table.h"
+#include "access/xact.h"
 #include "catalog/index.h"
 #include "commands/vacuum.h"
 #include "optimizer/paths.h"
@@ -35,6 +36,7 @@
 #include "storage/bufmgr.h"
 #include "tcop/tcopprot.h"
 #include "utils/lsyscache.h"
+#include "utils/rel.h"
 
 /*
  * DSM keys for parallel vacuum.  Unlike other parallel execution code, since
index c6d30fa5271c29f17b8cab0e984b8f93115fd143..f36c40e852ff80c8bd3ad606088d848fb34fb2c9 100644 (file)
  * Note that there can be more than one worker in a database concurrently.
  * They will store the table they are currently vacuuming in shared memory, so
  * that other workers avoid being blocked waiting for the vacuum lock for that
- * table.  They will also reload the pgstats data just before vacuuming each
- * table, to avoid vacuuming a table that was just finished being vacuumed by
- * another worker and thus is no longer noted in shared memory.  However,
- * there is a window (caused by pgstat delay) on which a worker may choose a
- * table that was already vacuumed; this is a bug in the current design.
+ * table.  They will also fetch the last time the table was vacuumed from
+ * pgstats just before vacuuming each table, to avoid vacuuming a table that
+ * was just finished being vacuumed by another worker and thus is no longer
+ * noted in shared memory.  However, there is a small window (due to not yet
+ * holding the relation lock) during which a worker may choose a table that was
+ * already vacuumed; this is a bug in the current design.
  *
  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -129,9 +130,6 @@ int                 autovacuum_vac_cost_limit;
 
 int                    Log_autovacuum_min_duration = 600000;
 
-/* how long to keep pgstat data in the launcher, in milliseconds */
-#define STATS_READ_DELAY 1000
-
 /* the minimum allowed time between two awakenings of the launcher */
 #define MIN_AUTOVAC_SLEEPTIME 100.0 /* milliseconds */
 #define MAX_AUTOVAC_SLEEPTIME 300      /* seconds */
@@ -342,15 +340,11 @@ static void autovacuum_do_vac_analyze(autovac_table *tab,
                                                                          BufferAccessStrategy bstrategy);
 static AutoVacOpts *extract_autovac_opts(HeapTuple tup,
                                                                                 TupleDesc pg_class_desc);
-static PgStat_StatTabEntry *get_pgstat_tabentry_relid(Oid relid, bool isshared,
-                                                                                                         PgStat_StatDBEntry *shared,
-                                                                                                         PgStat_StatDBEntry *dbentry);
 static void perform_work_item(AutoVacuumWorkItem *workitem);
 static void autovac_report_activity(autovac_table *tab);
 static void autovac_report_workitem(AutoVacuumWorkItem *workitem,
                                                                        const char *nspname, const char *relname);
 static void avl_sigusr2_handler(SIGNAL_ARGS);
-static void autovac_refresh_stats(void);
 
 
 
@@ -555,12 +549,6 @@ AutoVacLauncherMain(int argc, char *argv[])
                DatabaseListCxt = NULL;
                dlist_init(&DatabaseList);
 
-               /*
-                * Make sure pgstat also considers our stat data as gone.  Note: we
-                * mustn't use autovac_refresh_stats here.
-                */
-               pgstat_clear_snapshot();
-
                /* Now we can allow interrupts again */
                RESUME_INTERRUPTS();
 
@@ -611,6 +599,12 @@ AutoVacLauncherMain(int argc, char *argv[])
        SetConfigOption("default_transaction_isolation", "read committed",
                                        PGC_SUSET, PGC_S_OVERRIDE);
 
+       /*
+        * Even when system is configured to use a different fetch consistency,
+        * for autovac we always want fresh stats.
+        */
+       SetConfigOption("stats_fetch_consistency", "none", PGC_SUSET, PGC_S_OVERRIDE);
+
        /*
         * In emergency mode, just start a worker (unless shutdown was requested)
         * and go away.
@@ -963,9 +957,6 @@ rebuild_database_list(Oid newdb)
        HTAB       *dbhash;
        dlist_iter      iter;
 
-       /* use fresh stats */
-       autovac_refresh_stats();
-
        newcxt = AllocSetContextCreate(AutovacMemCxt,
                                                                   "Autovacuum database list",
                                                                   ALLOCSET_DEFAULT_SIZES);
@@ -1184,9 +1175,6 @@ do_start_worker(void)
                                                                   ALLOCSET_DEFAULT_SIZES);
        oldcxt = MemoryContextSwitchTo(tmpcxt);
 
-       /* use fresh stats */
-       autovac_refresh_stats();
-
        /* Get a list of databases */
        dblist = get_database_list();
 
@@ -1642,6 +1630,12 @@ AutoVacWorkerMain(int argc, char *argv[])
                SetConfigOption("synchronous_commit", "local",
                                                PGC_SUSET, PGC_S_OVERRIDE);
 
+       /*
+        * Even when system is configured to use a different fetch consistency,
+        * for autovac we always want fresh stats.
+        */
+       SetConfigOption("stats_fetch_consistency", "none", PGC_SUSET, PGC_S_OVERRIDE);
+
        /*
         * Get the info about the database we're going to work on.
         */
@@ -1966,8 +1960,6 @@ do_autovacuum(void)
        HASHCTL         ctl;
        HTAB       *table_toast_map;
        ListCell   *volatile cell;
-       PgStat_StatDBEntry *shared;
-       PgStat_StatDBEntry *dbentry;
        BufferAccessStrategy bstrategy;
        ScanKeyData key;
        TupleDesc       pg_class_desc;
@@ -1986,22 +1978,9 @@ do_autovacuum(void)
                                                                                  ALLOCSET_DEFAULT_SIZES);
        MemoryContextSwitchTo(AutovacMemCxt);
 
-       /*
-        * may be NULL if we couldn't find an entry (only happens if we are
-        * forcing a vacuum for anti-wrap purposes).
-        */
-       dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-
        /* Start a transaction so our commands have one to play into. */
        StartTransactionCommand();
 
-       /*
-        * Clean up any dead statistics entries for this DB. We always want to do
-        * this exactly once per DB-processing cycle, even if we find nothing
-        * worth vacuuming in the database.
-        */
-       pgstat_vacuum_stat();
-
        /*
         * Compute the multixact age for which freezing is urgent.  This is
         * normally autovacuum_multixact_freeze_max_age, but may be less if we are
@@ -2039,9 +2018,6 @@ do_autovacuum(void)
        /* StartTransactionCommand changed elsewhere */
        MemoryContextSwitchTo(AutovacMemCxt);
 
-       /* The database hash where pgstat keeps shared relations */
-       shared = pgstat_fetch_stat_dbentry(InvalidOid);
-
        classRel = table_open(RelationRelationId, AccessShareLock);
 
        /* create a copy so we can use it after closing pg_class */
@@ -2119,8 +2095,8 @@ do_autovacuum(void)
 
                /* Fetch reloptions and the pgstat entry for this table */
                relopts = extract_autovac_opts(tuple, pg_class_desc);
-               tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-                                                                                        shared, dbentry);
+               tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+                                                                                                 relid);
 
                /* Check if it needs vacuum or analyze */
                relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
@@ -2203,8 +2179,8 @@ do_autovacuum(void)
                }
 
                /* Fetch the pgstat entry for this table */
-               tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-                                                                                        shared, dbentry);
+               tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+                                                                                                 relid);
 
                relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
                                                                  effective_multixact_freeze_max_age,
@@ -2418,12 +2394,8 @@ do_autovacuum(void)
                /*
                 * Check whether pgstat data still says we need to vacuum this table.
                 * It could have changed if something else processed the table while
-                * we weren't looking.
-                *
-                * Note: we have a special case in pgstat code to ensure that the
-                * stats we read are as up-to-date as possible, to avoid the problem
-                * that somebody just finished vacuuming this table.  The window to
-                * the race condition is not closed but it is very small.
+                * we weren't looking. This doesn't entirely close the race condition,
+                * but it is very small.
                 */
                MemoryContextSwitchTo(AutovacMemCxt);
                tab = table_recheck_autovac(relid, table_toast_map, pg_class_desc,
@@ -2768,29 +2740,6 @@ extract_autovac_opts(HeapTuple tup, TupleDesc pg_class_desc)
        return av;
 }
 
-/*
- * get_pgstat_tabentry_relid
- *
- * Fetch the pgstat entry of a table, either local to a database or shared.
- */
-static PgStat_StatTabEntry *
-get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
-                                                 PgStat_StatDBEntry *dbentry)
-{
-       PgStat_StatTabEntry *tabentry = NULL;
-
-       if (isshared)
-       {
-               if (PointerIsValid(shared))
-                       tabentry = hash_search(shared->tables, &relid,
-                                                                  HASH_FIND, NULL);
-       }
-       else if (PointerIsValid(dbentry))
-               tabentry = hash_search(dbentry->tables, &relid,
-                                                          HASH_FIND, NULL);
-
-       return tabentry;
-}
 
 /*
  * table_recheck_autovac
@@ -2812,7 +2761,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
        autovac_table *tab = NULL;
        bool            wraparound;
        AutoVacOpts *avopts;
-       static bool reuse_stats = false;
 
        /* fetch the relation's relcache entry */
        classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
@@ -2836,35 +2784,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
                        avopts = &hentry->ar_reloptions;
        }
 
-       /*
-        * Reuse the stats to recheck whether a relation needs to be vacuumed or
-        * analyzed if it was reloaded before and has not been cleared yet. This
-        * is necessary to avoid frequent refresh of stats, especially when there
-        * are very large number of relations and the refresh can cause lots of
-        * overhead.
-        *
-        * If we determined that a relation needs to be vacuumed or analyzed,
-        * based on the old stats, we refresh stats and recheck the necessity
-        * again. Because a relation may have already been vacuumed or analyzed by
-        * someone since the last reload of stats.
-        */
-       if (reuse_stats)
-       {
-               recheck_relation_needs_vacanalyze(relid, avopts, classForm,
-                                                                                 effective_multixact_freeze_max_age,
-                                                                                 &dovacuum, &doanalyze, &wraparound);
-
-               /* Quick exit if a relation doesn't need to be vacuumed or analyzed */
-               if (!doanalyze && !dovacuum)
-               {
-                       heap_freetuple(classTup);
-                       return NULL;
-               }
-       }
-
-       /* Use fresh stats and recheck again */
-       autovac_refresh_stats();
-
        recheck_relation_needs_vacanalyze(relid, avopts, classForm,
                                                                          effective_multixact_freeze_max_age,
                                                                          &dovacuum, &doanalyze, &wraparound);
@@ -2962,21 +2881,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
                tab->at_dobalance =
                        !(avopts && (avopts->vacuum_cost_limit > 0 ||
                                                 avopts->vacuum_cost_delay > 0));
-
-               /*
-                * When we decide to do vacuum or analyze, the existing stats cannot
-                * be reused in the next cycle because it's cleared at the end of
-                * vacuum or analyze (by AtEOXact_PgStat()).
-                */
-               reuse_stats = false;
-       }
-       else
-       {
-               /*
-                * If neither vacuum nor analyze is necessary, the existing stats is
-                * not cleared and can be reused in the next cycle.
-                */
-               reuse_stats = true;
        }
 
        heap_freetuple(classTup);
@@ -3001,17 +2905,10 @@ recheck_relation_needs_vacanalyze(Oid relid,
                                                                  bool *wraparound)
 {
        PgStat_StatTabEntry *tabentry;
-       PgStat_StatDBEntry *shared = NULL;
-       PgStat_StatDBEntry *dbentry = NULL;
-
-       if (classForm->relisshared)
-               shared = pgstat_fetch_stat_dbentry(InvalidOid);
-       else
-               dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
 
        /* fetch the pgstat table entry */
-       tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-                                                                                shared, dbentry);
+       tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+                                                                                         relid);
 
        relation_needs_vacanalyze(relid, avopts, classForm, tabentry,
                                                          effective_multixact_freeze_max_age,
@@ -3169,11 +3066,11 @@ relation_needs_vacanalyze(Oid relid,
        }
 
        /*
-        * If we found the table in the stats hash, and autovacuum is currently
-        * enabled, make a threshold-based decision whether to vacuum and/or
-        * analyze.  If autovacuum is currently disabled, we must be here for
-        * anti-wraparound vacuuming only, so don't vacuum (or analyze) anything
-        * that's not being forced.
+        * If we found stats for the table, and autovacuum is currently enabled,
+        * make a threshold-based decision whether to vacuum and/or analyze.  If
+        * autovacuum is currently disabled, we must be here for anti-wraparound
+        * vacuuming only, so don't vacuum (or analyze) anything that's not being
+        * forced.
         */
        if (PointerIsValid(tabentry) && AutoVacuumingActive())
        {
@@ -3472,35 +3369,3 @@ AutoVacuumShmemInit(void)
        else
                Assert(found);
 }
-
-/*
- * autovac_refresh_stats
- *             Refresh pgstats data for an autovacuum process
- *
- * Cause the next pgstats read operation to obtain fresh data, but throttle
- * such refreshing in the autovacuum launcher.  This is mostly to avoid
- * rereading the pgstats files too many times in quick succession when there
- * are many databases.
- *
- * Note: we avoid throttling in the autovac worker, as it would be
- * counterproductive in the recheck logic.
- */
-static void
-autovac_refresh_stats(void)
-{
-       if (IsAutoVacuumLauncherProcess())
-       {
-               static TimestampTz last_read = 0;
-               TimestampTz current_time;
-
-               current_time = GetCurrentTimestamp();
-
-               if (!TimestampDifferenceExceeds(last_read, current_time,
-                                                                               STATS_READ_DELAY))
-                       return;
-
-               last_read = current_time;
-       }
-
-       pgstat_clear_snapshot();
-}
index e733c70368a7883348ddaff03d0887b060e72687..c937c39f5027b78aae37930644c5bc8dd9170ac1 100644 (file)
@@ -212,6 +212,16 @@ CheckpointerMain(void)
         */
        last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
 
+       /*
+        * Write out stats after shutdown. This needs to be called by exactly one
+        * process during a normal shutdown, and since checkpointer is shut down
+        * very late...
+        *
+        * Walsenders are shut down after the checkpointer, but currently don't
+        * report stats. If that changes, we need a more complicated solution.
+        */
+       before_shmem_exit(pgstat_before_server_shutdown, 0);
+
        /*
         * Create a memory context that we will do all our work in.  We do this so
         * that we can reset the context during error recovery and thereby avoid
@@ -358,7 +368,7 @@ CheckpointerMain(void)
                if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
                {
                        do_checkpoint = true;
-                       PendingCheckpointerStats.m_requested_checkpoints++;
+                       PendingCheckpointerStats.requested_checkpoints++;
                }
 
                /*
@@ -372,7 +382,7 @@ CheckpointerMain(void)
                if (elapsed_secs >= CheckPointTimeout)
                {
                        if (!do_checkpoint)
-                               PendingCheckpointerStats.m_timed_checkpoints++;
+                               PendingCheckpointerStats.timed_checkpoints++;
                        do_checkpoint = true;
                        flags |= CHECKPOINT_CAUSE_TIME;
                }
@@ -569,7 +579,7 @@ HandleCheckpointerInterrupts(void)
                 * updates the statistics, increment the checkpoint request and flush
                 * out pending statistic.
                 */
-               PendingCheckpointerStats.m_requested_checkpoints++;
+               PendingCheckpointerStats.requested_checkpoints++;
                ShutdownXLOG(0, 0);
                pgstat_report_checkpointer();
                pgstat_report_wal(true);
@@ -1262,9 +1272,9 @@ AbsorbSyncRequests(void)
        LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
        /* Transfer stats counts into pending pgstats message */
-       PendingCheckpointerStats.m_buf_written_backend
+       PendingCheckpointerStats.buf_written_backend
                += CheckpointerShmem->num_backend_writes;
-       PendingCheckpointerStats.m_buf_fsync_backend
+       PendingCheckpointerStats.buf_fsync_backend
                += CheckpointerShmem->num_backend_fsync;
 
        CheckpointerShmem->num_backend_writes = 0;
index 3f412dad2e62cec23b0c00563ba2836cd6394508..1aed2e2e99ea8805dc16df5818a5ff7efad5bfea 100644 (file)
@@ -98,9 +98,8 @@ SignalHandlerForCrashExit(SIGNAL_ARGS)
  * shut down and exit.
  *
  * Typically, this handler would be used for SIGTERM, but some processes use
- * other signals. In particular, the checkpointer exits on SIGUSR2, the
- * stats collector on SIGQUIT, and the WAL writer exits on either SIGINT
- * or SIGTERM.
+ * other signals. In particular, the checkpointer exits on SIGUSR2, and the
+ * WAL writer exits on either SIGINT or SIGTERM.
  *
  * ShutdownRequestPending should be checked at a convenient place within the
  * main loop, or else the main loop should call HandleMainLoopInterrupts.
index 20c4629e55ca82fbfd5fc3856601bcbc80fd4cec..a9f3a7ef492f311f47e7d3fe677fa95538b86135 100644 (file)
 /* ----------
  * pgstat.c
+ *       Infrastructure for the cumulative statistics system.
  *
- *     All the statistics collector stuff hacked up in one big, ugly file.
+ * The cumulative statistics system accumulates statistics for different kinds
+ * of objects. Some kinds of statistics are collected for a fixed number of
+ * objects (most commonly 1), e.g., checkpointer statistics. Other kinds of
+ * statistics are collected for a varying number of objects
+ * (e.g. relations). See PgStat_KindInfo for a list of currently handled
+ * statistics.
  *
- *     TODO:   - Separate collector, postmaster and backend stuff
- *                       into different files.
+ * Statistics are loaded from the filesystem during startup (by the startup
+ * process), unless preceded by a crash, in which case all stats are
+ * discarded. They are written out by the checkpointer process just before
+ * shutting down, except when shutting down in immediate mode.
  *
- *                     - Add some automatic call for pgstat vacuuming.
+ * Fixed-numbered stats are stored in plain (non-dynamic) shared memory.
  *
- *                     - Add a pgstat config column to pg_database, so this
- *                       entire thing can be enabled/disabled on a per db basis.
+ * Statistics for variable-numbered objects are stored in dynamic shared
+ * memory and can be found via a dshash hashtable. The statistics counters are
+ * not part of the dshash entry (PgStatShared_HashEntry) directly, but are
+ * separately allocated (PgStatShared_HashEntry->body). The separate
+ * allocation allows different kinds of statistics to be stored in the same
+ * hashtable without wasting space in PgStatShared_HashEntry.
  *
- *     Copyright (c) 2001-2022, PostgreSQL Global Development Group
+ * Variable-numbered stats are addressed by PgStat_HashKey while running.  It
+ * is not possible to have statistics for an object that cannot be addressed
+ * that way at runtime. A wider identifier can be used when serializing to
+ * disk (used for replication slot stats).
  *
- *     src/backend/postmaster/pgstat.c
+ * To avoid contention on the shared hashtable, each backend has a
+ * backend-local hashtable (pgStatEntryRefHash) in front of the shared
+ * hashtable, containing references (PgStat_EntryRef) to shared hashtable
+ * entries. The shared hashtable only needs to be accessed when no prior
+ * reference is found in the local hashtable. Besides pointing to the the
+ * shared hashtable entry (PgStatShared_HashEntry) PgStat_EntryRef also
+ * contains a pointer to the the shared statistics data, as a process-local
+ * address, to reduce access costs.
+ *
+ * The names for structs stored in shared memory are prefixed with
+ * PgStatShared instead of PgStat. Each stats entry in shared memory is
+ * protected by a dedicated lwlock.
+ *
+ * Most stats updates are first accumulated locally in each process as pending
+ * entries, then later flushed to shared memory (just after commit, or by
+ * idle-timeout). This practically eliminates contention on individual stats
+ * entries. For most kinds of variable-numbered pending stats data is stored
+ * in PgStat_EntryRef->pending. All entries with pending data are in the
+ * pgStatPending list. Pending statistics updates are flushed out by
+ * pgstat_report_stat().
+ *
+ * The behavior of different kinds of statistics is determined by the kind's
+ * entry in pgstat_kind_infos, see PgStat_KindInfo for details.
+ *
+ * The consistency of read accesses to statistics can be configured using the
+ * stats_fetch_consistency GUC (see config.sgml and monitoring.sgml for the
+ * settings). When using PGSTAT_FETCH_CONSISTENCY_CACHE or
+ * PGSTAT_FETCH_CONSISTENCY_SNAPSHOT statistics are stored in
+ * pgStatLocal.snapshot.
+ *
+ * To keep things manageable, stats handling is split across several
+ * files. Infrastructure pieces are in:
+ * - pgstat.c - this file, to tie it all together
+ * - pgstat_shmem.c - nearly everything dealing with shared memory, including
+ *   the maintenance of hashtable entries
+ * - pgstat_xact.c - transactional integration, including the transactional
+ *   creation and dropping of stats entries
+ *
+ * Each statistics kind is handled in a dedicated file:
+ * - pgstat_archiver.c
+ * - pgstat_bgwriter.c
+ * - pgstat_checkpointer.c
+ * - pgstat_database.c
+ * - pgstat_function.c
+ * - pgstat_relation.c
+ * - pgstat_slru.c
+ * - pgstat_subscription.c
+ * - pgstat_wal.c
+ *
+ * Whenever possible infrastructure files should not contain code related to
+ * specific kinds of stats.
+ *
+ *
+ * Copyright (c) 2001-2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *       src/backend/postmaster/pgstat.c
  * ----------
  */
 #include "postgres.h"
 
 #include <unistd.h>
-#include <fcntl.h>
-#include <sys/param.h>
-#include <sys/time.h>
-#include <sys/socket.h>
-#include <netdb.h>
-#include <netinet/in.h>
-#include <arpa/inet.h>
-#include <signal.h>
-#include <time.h>
-#ifdef HAVE_SYS_SELECT_H
-#include <sys/select.h>
-#endif
 
-#include "access/heapam.h"
-#include "access/htup_details.h"
-#include "access/tableam.h"
 #include "access/transam.h"
 #include "access/xact.h"
-#include "catalog/catalog.h"
-#include "catalog/pg_database.h"
-#include "catalog/pg_proc.h"
-#include "catalog/pg_subscription.h"
-#include "common/ip.h"
-#include "libpq/libpq.h"
-#include "libpq/pqsignal.h"
-#include "mb/pg_wchar.h"
-#include "miscadmin.h"
+#include "lib/dshash.h"
 #include "pgstat.h"
-#include "postmaster/autovacuum.h"
-#include "postmaster/fork_process.h"
-#include "postmaster/interrupt.h"
-#include "postmaster/postmaster.h"
-#include "replication/slot.h"
-#include "replication/walsender.h"
-#include "storage/backendid.h"
-#include "storage/dsm.h"
+#include "port/atomics.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
-#include "storage/latch.h"
-#include "storage/lmgr.h"
+#include "storage/lwlock.h"
 #include "storage/pg_shmem.h"
-#include "storage/proc.h"
-#include "storage/procsignal.h"
-#include "utils/builtins.h"
+#include "storage/shmem.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/pgstat_internal.h"
-#include "utils/ps_status.h"
-#include "utils/rel.h"
-#include "utils/snapmgr.h"
 #include "utils/timestamp.h"
 
 
 /* ----------
  * Timer definitions.
+ *
+ * In milliseconds.
+ * ----------
+ */
+
+/* minimum interval non-forced stats flushes.*/
+#define PGSTAT_MIN_INTERVAL                    1000
+/* how long until to block flushing pending stats updates */
+#define PGSTAT_MAX_INTERVAL                    60000
+/* when to call pgstat_report_stat() again, even when idle */
+#define PGSTAT_IDLE_INTERVAL           10000
+
+/* ----------
+ * Initial size hints for the hash tables used in statistics.
  * ----------
  */
 
-#define PGSTAT_RETRY_DELAY             10      /* How long to wait between checks for a
-                                                                        * new file; in milliseconds. */
+#define PGSTAT_SNAPSHOT_HASH_SIZE      512
 
-#define PGSTAT_MAX_WAIT_TIME   10000   /* Maximum time to wait for a stats
-                                                                                * file update; in milliseconds. */
 
-#define PGSTAT_INQ_INTERVAL            640 /* How often to ping the collector for a
-                                                                        * new file; in milliseconds. */
+/* hash table for statistics snapshots entry */
+typedef struct PgStat_SnapshotEntry
+{
+       PgStat_HashKey key;
+       char            status;                 /* for simplehash use */
+       void       *data;                       /* the stats data itself */
+} PgStat_SnapshotEntry;
 
-#define PGSTAT_RESTART_INTERVAL 60     /* How often to attempt to restart a
-                                                                        * failed statistics collector; in
-                                                                        * seconds. */
 
-#define PGSTAT_POLL_LOOP_COUNT (PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)
-#define PGSTAT_INQ_LOOP_COUNT  (PGSTAT_INQ_INTERVAL / PGSTAT_RETRY_DELAY)
+/* ----------
+ * Backend-local Hash Table Definitions
+ * ----------
+ */
 
-/* Minimum receive buffer size for the collector's socket. */
-#define PGSTAT_MIN_RCVBUF              (100 * 1024)
+/* for stats snapshot entries */
+#define SH_PREFIX pgstat_snapshot
+#define SH_ELEMENT_TYPE PgStat_SnapshotEntry
+#define SH_KEY_TYPE PgStat_HashKey
+#define SH_KEY key
+#define SH_HASH_KEY(tb, key) \
+       pgstat_hash_hash_key(&key, sizeof(PgStat_HashKey), NULL)
+#define SH_EQUAL(tb, a, b) \
+       pgstat_cmp_hash_key(&a, &b, sizeof(PgStat_HashKey), NULL) == 0
+#define SH_SCOPE static inline
+#define SH_DEFINE
+#define SH_DECLARE
+#include "lib/simplehash.h"
 
 
 /* ----------
  * ----------
  */
 
-#ifdef EXEC_BACKEND
-static pid_t pgstat_forkexec(void);
-#endif
+static void pgstat_write_statsfile(void);
+static void pgstat_read_statsfile(void);
+
+static void pgstat_reset_after_failure(TimestampTz ts);
+
+static bool pgstat_flush_pending_entries(bool nowait);
 
-NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
-
-static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
-static PgStat_StatTabEntry *pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry,
-                                                                                                Oid tableoid, bool create);
-static PgStat_StatSubEntry *pgstat_get_subscription_entry(Oid subid, bool create);
-static void pgstat_reset_subscription(PgStat_StatSubEntry *subentry, TimestampTz ts);
-static void pgstat_write_statsfiles(bool permanent, bool allDbs);
-static void pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent);
-static HTAB *pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep);
-static void pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
-                                                                        bool permanent);
-static void backend_read_statsfile(void);
-
-static bool pgstat_write_statsfile_needed(void);
-static bool pgstat_db_requested(Oid databaseid);
-
-static PgStat_StatReplSlotEntry *pgstat_get_replslot_entry(NameData name, bool create_it);
-static void pgstat_reset_replslot_entry(PgStat_StatReplSlotEntry *slotstats, TimestampTz ts);
-
-static HTAB *pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid);
-
-static void pgstat_setup_memcxt(void);
-
-static void pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len);
-static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
-static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
-static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
-static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
-static void pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len);
-static void pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len);
-static void pgstat_recv_resetslrucounter(PgStat_MsgResetslrucounter *msg, int len);
-static void pgstat_recv_resetreplslotcounter(PgStat_MsgResetreplslotcounter *msg, int len);
-static void pgstat_recv_resetsubcounter(PgStat_MsgResetsubcounter *msg, int len);
-static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
-static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
-static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
-static void pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len);
-static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
-static void pgstat_recv_checkpointer(PgStat_MsgCheckpointer *msg, int len);
-static void pgstat_recv_wal(PgStat_MsgWal *msg, int len);
-static void pgstat_recv_slru(PgStat_MsgSLRU *msg, int len);
-static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
-static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
-static void pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len);
-static void pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len);
-static void pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len);
-static void pgstat_recv_connect(PgStat_MsgConnect *msg, int len);
-static void pgstat_recv_disconnect(PgStat_MsgDisconnect *msg, int len);
-static void pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len);
-static void pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len);
-static void pgstat_recv_subscription_drop(PgStat_MsgSubscriptionDrop *msg, int len);
-static void pgstat_recv_subscription_error(PgStat_MsgSubscriptionError *msg, int len);
+static void pgstat_prep_snapshot(void);
+static void pgstat_build_snapshot(void);
+static void pgstat_build_snapshot_fixed(PgStat_Kind kind);
+
+static inline bool pgstat_is_kind_valid(int ikind);
 
 
 /* ----------
@@ -167,6 +183,7 @@ static void pgstat_recv_subscription_error(PgStat_MsgSubscriptionError *msg, int
  */
 
 bool           pgstat_track_counts = false;
+int                    pgstat_fetch_consistency = PGSTAT_FETCH_CONSISTENCY_NONE;
 
 
 /* ----------
@@ -184,44 +201,33 @@ char         *pgstat_stat_tmpname = NULL;
  * ----------
  */
 
-pgsocket       pgStatSock = PGINVALID_SOCKET;
+PgStat_LocalState pgStatLocal;
 
 
 /* ----------
  * Local data
+ *
+ * NB: There should be only variables related to stats infrastructure here,
+ * not for specific kinds of stats.
  * ----------
  */
 
-static struct sockaddr_storage pgStatAddr;
-
-static time_t last_pgstat_start_time;
-
-static bool pgStatRunningInCollector = false;
-
 /*
- * Info about current "snapshot" of stats file
+ * Memory contexts containing the pgStatEntryRefHash table, the
+ * pgStatSharedRef entries, and pending data respectively. Mostly to make it
+ * easier to track / attribute memory usage.
  */
-static MemoryContext pgStatLocalContext = NULL;
-static HTAB *pgStatDBHash = NULL;
 
-/*
- * Cluster wide statistics, kept in the stats collector.
- * Contains statistics that are not collected per database
- * or per table.
- */
-static PgStat_ArchiverStats archiverStats;
-static PgStat_GlobalStats globalStats;
-static PgStat_WalStats walStats;
-static PgStat_SLRUStats slruStats[SLRU_NUM_ELEMENTS];
-static HTAB *replSlotStatHash = NULL;
-static HTAB *subscriptionStatHash = NULL;
+static MemoryContext pgStatPendingContext = NULL;
 
 /*
- * List of OIDs of databases we need to write out.  If an entry is InvalidOid,
- * it means to write only the shared-catalog stats ("DB 0"); otherwise, we
- * will write both that DB's data and the shared stats.
+ * Backend local list of PgStat_EntryRef with unflushed pending stats.
+ *
+ * Newly pending entries should only ever be added to the end of the list,
+ * otherwise pgstat_flush_pending_entries() might not see them immediately.
  */
-static List *pending_write_requests = NIL;
+static dlist_head pgStatPending = DLIST_STATIC_INIT(pgStatPending);
+
 
 /*
  * For assertions that check pgstat is not used before initialization / after
@@ -233,455 +239,234 @@ static bool pgstat_is_shutdown = false;
 #endif
 
 
-/* ------------------------------------------------------------
- * Public functions called from postmaster follow
- * ------------------------------------------------------------
- */
-
 /*
- * Called from postmaster at startup. Create the resources required
- * by the statistics collector process.  If unable to do so, do not
- * fail --- better to let the postmaster start with stats collection
- * disabled.
+ * The different kinds of statistics.
+ *
+ * If reasonably possible, handling specific to one kind of stats should go
+ * through this abstraction, rather than making more of pgstat.c aware.
+ *
+ * See comments for struct PgStat_KindInfo for details about the individual
+ * fields.
+ *
+ * XXX: It'd be nicer to define this outside of this file. But there doesn't
+ * seem to be a great way of doing that, given the split across multiple
+ * files.
  */
-void
-pgstat_init(void)
-{
-       socklen_t       alen;
-       struct addrinfo *addrs = NULL,
-                          *addr,
-                               hints;
-       int                     ret;
-       fd_set          rset;
-       struct timeval tv;
-       char            test_byte;
-       int                     sel_res;
-       int                     tries = 0;
+static const PgStat_KindInfo pgstat_kind_infos[PGSTAT_NUM_KINDS] = {
 
-#define TESTBYTEVAL ((char) 199)
+       /* stats kinds for variable-numbered objects */
 
-       /*
-        * This static assertion verifies that we didn't mess up the calculations
-        * involved in selecting maximum payload sizes for our UDP messages.
-        * Because the only consequence of overrunning PGSTAT_MAX_MSG_SIZE would
-        * be silent performance loss from fragmentation, it seems worth having a
-        * compile-time cross-check that we didn't.
-        */
-       StaticAssertStmt(sizeof(PgStat_Msg) <= PGSTAT_MAX_MSG_SIZE,
-                                        "maximum stats message size exceeds PGSTAT_MAX_MSG_SIZE");
+       [PGSTAT_KIND_DATABASE] = {
+               .name = "database",
 
-       /*
-        * Create the UDP socket for sending and receiving statistic messages
-        */
-       hints.ai_flags = AI_PASSIVE;
-       hints.ai_family = AF_UNSPEC;
-       hints.ai_socktype = SOCK_DGRAM;
-       hints.ai_protocol = 0;
-       hints.ai_addrlen = 0;
-       hints.ai_addr = NULL;
-       hints.ai_canonname = NULL;
-       hints.ai_next = NULL;
-       ret = pg_getaddrinfo_all("localhost", NULL, &hints, &addrs);
-       if (ret || !addrs)
-       {
-               ereport(LOG,
-                               (errmsg("could not resolve \"localhost\": %s",
-                                               gai_strerror(ret))));
-               goto startup_failed;
-       }
+               .fixed_amount = false,
+               /* so pg_stat_database entries can be seen in all databases */
+               .accessed_across_databases = true,
 
-       /*
-        * On some platforms, pg_getaddrinfo_all() may return multiple addresses
-        * only one of which will actually work (eg, both IPv6 and IPv4 addresses
-        * when kernel will reject IPv6).  Worse, the failure may occur at the
-        * bind() or perhaps even connect() stage.  So we must loop through the
-        * results till we find a working combination. We will generate LOG
-        * messages, but no error, for bogus combinations.
-        */
-       for (addr = addrs; addr; addr = addr->ai_next)
-       {
-#ifdef HAVE_UNIX_SOCKETS
-               /* Ignore AF_UNIX sockets, if any are returned. */
-               if (addr->ai_family == AF_UNIX)
-                       continue;
-#endif
+               .shared_size = sizeof(PgStatShared_Database),
+               .shared_data_off = offsetof(PgStatShared_Database, stats),
+               .shared_data_len = sizeof(((PgStatShared_Database *) 0)->stats),
+               .pending_size = sizeof(PgStat_StatDBEntry),
 
-               if (++tries > 1)
-                       ereport(LOG,
-                                       (errmsg("trying another address for the statistics collector")));
+               .flush_pending_cb = pgstat_database_flush_cb,
+               .reset_timestamp_cb = pgstat_database_reset_timestamp_cb,
+       },
 
-               /*
-                * Create the socket.
-                */
-               if ((pgStatSock = socket(addr->ai_family, SOCK_DGRAM, 0)) == PGINVALID_SOCKET)
-               {
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not create socket for statistics collector: %m")));
-                       continue;
-               }
+       [PGSTAT_KIND_RELATION] = {
+               .name = "relation",
 
-               /*
-                * Bind it to a kernel assigned port on localhost and get the assigned
-                * port via getsockname().
-                */
-               if (bind(pgStatSock, addr->ai_addr, addr->ai_addrlen) < 0)
-               {
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not bind socket for statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .fixed_amount = false,
 
-               alen = sizeof(pgStatAddr);
-               if (getsockname(pgStatSock, (struct sockaddr *) &pgStatAddr, &alen) < 0)
-               {
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not get address of socket for statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .shared_size = sizeof(PgStatShared_Relation),
+               .shared_data_off = offsetof(PgStatShared_Relation, stats),
+               .shared_data_len = sizeof(((PgStatShared_Relation *) 0)->stats),
+               .pending_size = sizeof(PgStat_TableStatus),
 
-               /*
-                * Connect the socket to its own address.  This saves a few cycles by
-                * not having to respecify the target address on every send. This also
-                * provides a kernel-level check that only packets from this same
-                * address will be received.
-                */
-               if (connect(pgStatSock, (struct sockaddr *) &pgStatAddr, alen) < 0)
-               {
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not connect socket for statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .flush_pending_cb = pgstat_relation_flush_cb,
+               .delete_pending_cb = pgstat_relation_delete_pending_cb,
+       },
 
-               /*
-                * Try to send and receive a one-byte test message on the socket. This
-                * is to catch situations where the socket can be created but will not
-                * actually pass data (for instance, because kernel packet filtering
-                * rules prevent it).
-                */
-               test_byte = TESTBYTEVAL;
+       [PGSTAT_KIND_FUNCTION] = {
+               .name = "function",
 
-retry1:
-               if (send(pgStatSock, &test_byte, 1, 0) != 1)
-               {
-                       if (errno == EINTR)
-                               goto retry1;    /* if interrupted, just retry */
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not send test message on socket for statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .fixed_amount = false,
 
-               /*
-                * There could possibly be a little delay before the message can be
-                * received.  We arbitrarily allow up to half a second before deciding
-                * it's broken.
-                */
-               for (;;)                                /* need a loop to handle EINTR */
-               {
-                       FD_ZERO(&rset);
-                       FD_SET(pgStatSock, &rset);
-
-                       tv.tv_sec = 0;
-                       tv.tv_usec = 500000;
-                       sel_res = select(pgStatSock + 1, &rset, NULL, NULL, &tv);
-                       if (sel_res >= 0 || errno != EINTR)
-                               break;
-               }
-               if (sel_res < 0)
-               {
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("select() failed in statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
-               if (sel_res == 0 || !FD_ISSET(pgStatSock, &rset))
-               {
-                       /*
-                        * This is the case we actually think is likely, so take pains to
-                        * give a specific message for it.
-                        *
-                        * errno will not be set meaningfully here, so don't use it.
-                        */
-                       ereport(LOG,
-                                       (errcode(ERRCODE_CONNECTION_FAILURE),
-                                        errmsg("test message did not get through on socket for statistics collector")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .shared_size = sizeof(PgStatShared_Function),
+               .shared_data_off = offsetof(PgStatShared_Function, stats),
+               .shared_data_len = sizeof(((PgStatShared_Function *) 0)->stats),
+               .pending_size = sizeof(PgStat_BackendFunctionEntry),
 
-               test_byte++;                    /* just make sure variable is changed */
+               .flush_pending_cb = pgstat_function_flush_cb,
+       },
 
-retry2:
-               if (recv(pgStatSock, &test_byte, 1, 0) != 1)
-               {
-                       if (errno == EINTR)
-                               goto retry2;    /* if interrupted, just retry */
-                       ereport(LOG,
-                                       (errcode_for_socket_access(),
-                                        errmsg("could not receive test message on socket for statistics collector: %m")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+       [PGSTAT_KIND_REPLSLOT] = {
+               .name = "replslot",
 
-               if (test_byte != TESTBYTEVAL)   /* strictly paranoia ... */
-               {
-                       ereport(LOG,
-                                       (errcode(ERRCODE_INTERNAL_ERROR),
-                                        errmsg("incorrect test message transmission on socket for statistics collector")));
-                       closesocket(pgStatSock);
-                       pgStatSock = PGINVALID_SOCKET;
-                       continue;
-               }
+               .fixed_amount = false,
 
-               /* If we get here, we have a working socket */
-               break;
-       }
+               .accessed_across_databases = true,
+               .named_on_disk = true,
 
-       /* Did we find a working address? */
-       if (!addr || pgStatSock == PGINVALID_SOCKET)
-               goto startup_failed;
+               .shared_size = sizeof(PgStatShared_ReplSlot),
+               .shared_data_off = offsetof(PgStatShared_ReplSlot, stats),
+               .shared_data_len = sizeof(((PgStatShared_ReplSlot *) 0)->stats),
 
-       /*
-        * Set the socket to non-blocking IO.  This ensures that if the collector
-        * falls behind, statistics messages will be discarded; backends won't
-        * block waiting to send messages to the collector.
-        */
-       if (!pg_set_noblock(pgStatSock))
-       {
-               ereport(LOG,
-                               (errcode_for_socket_access(),
-                                errmsg("could not set statistics collector socket to nonblocking mode: %m")));
-               goto startup_failed;
-       }
+               .reset_timestamp_cb = pgstat_replslot_reset_timestamp_cb,
+               .to_serialized_name = pgstat_replslot_to_serialized_name_cb,
+               .from_serialized_name = pgstat_replslot_from_serialized_name_cb,
+       },
 
-       /*
-        * Try to ensure that the socket's receive buffer is at least
-        * PGSTAT_MIN_RCVBUF bytes, so that it won't easily overflow and lose
-        * data.  Use of UDP protocol means that we are willing to lose data under
-        * heavy load, but we don't want it to happen just because of ridiculously
-        * small default buffer sizes (such as 8KB on older Windows versions).
-        */
-       {
-               int                     old_rcvbuf;
-               int                     new_rcvbuf;
-               socklen_t       rcvbufsize = sizeof(old_rcvbuf);
+       [PGSTAT_KIND_SUBSCRIPTION] = {
+               .name = "subscription",
 
-               if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-                                          (char *) &old_rcvbuf, &rcvbufsize) < 0)
-               {
-                       ereport(LOG,
-                                       (errmsg("%s(%s) failed: %m", "getsockopt", "SO_RCVBUF")));
-                       /* if we can't get existing size, always try to set it */
-                       old_rcvbuf = 0;
-               }
+               .fixed_amount = false,
+               /* so pg_stat_subscription_stats entries can be seen in all databases */
+               .accessed_across_databases = true,
 
-               new_rcvbuf = PGSTAT_MIN_RCVBUF;
-               if (old_rcvbuf < new_rcvbuf)
-               {
-                       if (setsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-                                                  (char *) &new_rcvbuf, sizeof(new_rcvbuf)) < 0)
-                               ereport(LOG,
-                                               (errmsg("%s(%s) failed: %m", "setsockopt", "SO_RCVBUF")));
-               }
-       }
+               .shared_size = sizeof(PgStatShared_Subscription),
+               .shared_data_off = offsetof(PgStatShared_Subscription, stats),
+               .shared_data_len = sizeof(((PgStatShared_Subscription *) 0)->stats),
+               .pending_size = sizeof(PgStat_BackendSubEntry),
 
-       pg_freeaddrinfo_all(hints.ai_family, addrs);
+               .flush_pending_cb = pgstat_subscription_flush_cb,
+               .reset_timestamp_cb = pgstat_subscription_reset_timestamp_cb,
+       },
 
-       /* Now that we have a long-lived socket, tell fd.c about it. */
-       ReserveExternalFD();
 
-       return;
+       /* stats for fixed-numbered (mostly 1) objects */
 
-startup_failed:
-       ereport(LOG,
-                       (errmsg("disabling statistics collector for lack of working socket")));
+       [PGSTAT_KIND_ARCHIVER] = {
+               .name = "archiver",
 
-       if (addrs)
-               pg_freeaddrinfo_all(hints.ai_family, addrs);
+               .fixed_amount = true,
 
-       if (pgStatSock != PGINVALID_SOCKET)
-               closesocket(pgStatSock);
-       pgStatSock = PGINVALID_SOCKET;
+               .reset_all_cb = pgstat_archiver_reset_all_cb,
+               .snapshot_cb = pgstat_archiver_snapshot_cb,
+       },
 
-       /*
-        * Adjust GUC variables to suppress useless activity, and for debugging
-        * purposes (seeing track_counts off is a clue that we failed here). We
-        * use PGC_S_OVERRIDE because there is no point in trying to turn it back
-        * on from postgresql.conf without a restart.
-        */
-       SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
-}
+       [PGSTAT_KIND_BGWRITER] = {
+               .name = "bgwriter",
 
-/*
- * subroutine for pgstat_reset_all
- */
-static void
-pgstat_reset_remove_files(const char *directory)
-{
-       DIR                *dir;
-       struct dirent *entry;
-       char            fname[MAXPGPATH * 2];
+               .fixed_amount = true,
 
-       dir = AllocateDir(directory);
-       while ((entry = ReadDir(dir, directory)) != NULL)
-       {
-               int                     nchars;
-               Oid                     tmp_oid;
+               .reset_all_cb = pgstat_bgwriter_reset_all_cb,
+               .snapshot_cb = pgstat_bgwriter_snapshot_cb,
+       },
 
-               /*
-                * Skip directory entries that don't match the file names we write.
-                * See get_dbstat_filename for the database-specific pattern.
-                */
-               if (strncmp(entry->d_name, "global.", 7) == 0)
-                       nchars = 7;
-               else
-               {
-                       nchars = 0;
-                       (void) sscanf(entry->d_name, "db_%u.%n",
-                                                 &tmp_oid, &nchars);
-                       if (nchars <= 0)
-                               continue;
-                       /* %u allows leading whitespace, so reject that */
-                       if (strchr("0123456789", entry->d_name[3]) == NULL)
-                               continue;
-               }
+       [PGSTAT_KIND_CHECKPOINTER] = {
+               .name = "checkpointer",
 
-               if (strcmp(entry->d_name + nchars, "tmp") != 0 &&
-                       strcmp(entry->d_name + nchars, "stat") != 0)
-                       continue;
+               .fixed_amount = true,
+
+               .reset_all_cb = pgstat_checkpointer_reset_all_cb,
+               .snapshot_cb = pgstat_checkpointer_snapshot_cb,
+       },
+
+       [PGSTAT_KIND_SLRU] = {
+               .name = "slru",
+
+               .fixed_amount = true,
+
+               .reset_all_cb = pgstat_slru_reset_all_cb,
+               .snapshot_cb = pgstat_slru_snapshot_cb,
+       },
+
+       [PGSTAT_KIND_WAL] = {
+               .name = "wal",
+
+               .fixed_amount = true,
+
+               .reset_all_cb = pgstat_wal_reset_all_cb,
+               .snapshot_cb = pgstat_wal_snapshot_cb,
+       },
+};
 
-               snprintf(fname, sizeof(fname), "%s/%s", directory,
-                                entry->d_name);
-               unlink(fname);
-       }
-       FreeDir(dir);
-}
+
+/* ------------------------------------------------------------
+ * Functions managing the state of the stats system for all backends.
+ * ------------------------------------------------------------
+ */
 
 /*
- * Remove the stats files.  This is currently used only if WAL
- * recovery is needed after a crash.
+ * Read on-disk stats into memory at server start.
+ *
+ * Should only be called by the startup process or in single user mode.
  */
 void
-pgstat_reset_all(void)
+pgstat_restore_stats(void)
 {
-       pgstat_reset_remove_files(pgstat_stat_directory);
-       pgstat_reset_remove_files(PGSTAT_STAT_PERMANENT_DIRECTORY);
+       pgstat_read_statsfile();
 }
 
-#ifdef EXEC_BACKEND
-
 /*
- * Format up the arglist for, then fork and exec, statistics collector process
+ * Remove the stats file.  This is currently used only if WAL recovery is
+ * needed after a crash.
+ *
+ * Should only be called by the startup process or in single user mode.
  */
-static pid_t
-pgstat_forkexec(void)
+void
+pgstat_discard_stats(void)
 {
-       char       *av[10];
-       int                     ac = 0;
-
-       av[ac++] = "postgres";
-       av[ac++] = "--forkcol";
-       av[ac++] = NULL;                        /* filled in by postmaster_forkexec */
+       int                     ret;
 
-       av[ac] = NULL;
-       Assert(ac < lengthof(av));
+       /* NB: this needs to be done even in single user mode */
 
-       return postmaster_forkexec(ac, av);
+       ret = unlink(PGSTAT_STAT_PERMANENT_FILENAME);
+       if (ret != 0)
+       {
+               if (errno == ENOENT)
+                       elog(DEBUG2,
+                                "didn't need to unlink permanent stats file \"%s\" - didn't exist",
+                                PGSTAT_STAT_PERMANENT_FILENAME);
+               else
+                       ereport(LOG,
+                                       (errcode_for_file_access(),
+                                        errmsg("could not unlink permanent statistics file \"%s\": %m",
+                                                       PGSTAT_STAT_PERMANENT_FILENAME)));
+       }
+       else
+       {
+               ereport(DEBUG2,
+                               (errcode_for_file_access(),
+                                errmsg("unlinked permanent statistics file \"%s\"",
+                                               PGSTAT_STAT_PERMANENT_FILENAME)));
+       }
 }
-#endif                                                 /* EXEC_BACKEND */
-
 
 /*
- * Called from postmaster at startup or after an existing collector
- * died.  Attempt to fire up a fresh statistics collector.
+ * pgstat_before_server_shutdown() needs to be called by exactly one process
+ * during regular server shutdowns. Otherwise all stats will be lost.
  *
- * Returns PID of child process, or 0 if fail.
- *
- * Note: if fail, we will be called again from the postmaster main loop.
+ * We currently only write out stats for proc_exit(0). We might want to change
+ * that at some point... But right now pgstat_discard_stats() would be called
+ * during the start after a disorderly shutdown, anyway.
  */
-int
-pgstat_start(void)
+void
+pgstat_before_server_shutdown(int code, Datum arg)
 {
-       time_t          curtime;
-       pid_t           pgStatPid;
+       Assert(pgStatLocal.shmem != NULL);
+       Assert(!pgStatLocal.shmem->is_shutdown);
 
        /*
-        * Check that the socket is there, else pgstat_init failed and we can do
-        * nothing useful.
+        * Stats should only be reported after pgstat_initialize() and before
+        * pgstat_shutdown(). This is a convenient point to catch most violations
+        * of this rule.
         */
-       if (pgStatSock == PGINVALID_SOCKET)
-               return 0;
+       Assert(pgstat_is_initialized && !pgstat_is_shutdown);
 
-       /*
-        * Do nothing if too soon since last collector start.  This is a safety
-        * valve to protect against continuous respawn attempts if the collector
-        * is dying immediately at launch.  Note that since we will be re-called
-        * from the postmaster main loop, we will get another chance later.
-        */
-       curtime = time(NULL);
-       if ((unsigned int) (curtime - last_pgstat_start_time) <
-               (unsigned int) PGSTAT_RESTART_INTERVAL)
-               return 0;
-       last_pgstat_start_time = curtime;
+       /* flush out our own pending changes before writing out */
+       pgstat_report_stat(true);
 
        /*
-        * Okay, fork off the collector.
+        * Only write out file during normal shutdown. Don't even signal that
+        * we've shutdown during irregular shutdowns, because the shutdown
+        * sequence isn't coordinated to ensure this backend shuts down last.
         */
-#ifdef EXEC_BACKEND
-       switch ((pgStatPid = pgstat_forkexec()))
-#else
-       switch ((pgStatPid = fork_process()))
-#endif
+       if (code == 0)
        {
-               case -1:
-                       ereport(LOG,
-                                       (errmsg("could not fork statistics collector: %m")));
-                       return 0;
-
-#ifndef EXEC_BACKEND
-               case 0:
-                       /* in postmaster child ... */
-                       InitPostmasterChild();
-
-                       /* Close the postmaster's sockets */
-                       ClosePostmasterPorts(false);
-
-                       /* Drop our connection to postmaster's shared memory, as well */
-                       dsm_detach_all();
-                       PGSharedMemoryDetach();
-
-                       PgstatCollectorMain(0, NULL);
-                       break;
-#endif
-
-               default:
-                       return (int) pgStatPid;
+               pgStatLocal.shmem->is_shutdown = true;
+               pgstat_write_statsfile();
        }
-
-       /* shouldn't get here */
-       return 0;
-}
-
-void
-allow_immediate_pgstat_restart(void)
-{
-       last_pgstat_start_time = 0;
 }
 
 
@@ -701,6 +486,7 @@ static void
 pgstat_shutdown_hook(int code, Datum arg)
 {
        Assert(!pgstat_is_shutdown);
+       Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
 
        /*
         * If we got as far as discovering our own database ID, we can flush out
@@ -709,7 +495,15 @@ pgstat_shutdown_hook(int code, Datum arg)
         * failed backend starts might never get counted.)
         */
        if (OidIsValid(MyDatabaseId))
-               pgstat_report_stat(true);
+               pgstat_report_disconnect(MyDatabaseId);
+
+       pgstat_report_stat(true);
+
+       /* there shouldn't be any pending changes left */
+       Assert(dlist_is_empty(&pgStatPending));
+       dlist_init(&pgStatPending);
+
+       pgstat_detach_shmem();
 
 #ifdef USE_ASSERT_CHECKING
        pgstat_is_shutdown = true;
@@ -727,6 +521,8 @@ pgstat_initialize(void)
 {
        Assert(!pgstat_is_initialized);
 
+       pgstat_attach_shmem();
+
        pgstat_init_wal();
 
        /* Set up a process-exit hook to clean up */
@@ -745,717 +541,613 @@ pgstat_initialize(void)
 
 /*
  * Must be called by processes that performs DML: tcop/postgres.c, logical
- * receiver processes, SPI worker, etc. to send the so far collected
- * per-table and function usage statistics to the collector.  Note that this
- * is called only when not within a transaction, so it is fair to use
- * transaction stop time as an approximation of current time.
+ * receiver processes, SPI worker, etc. to flush pending statistics updates to
+ * shared memory.
+ *
+ * Unless called with 'force', pending stats updates are flushed happen once
+ * per PGSTAT_MIN_INTERVAL (1000ms). When not forced, stats flushes do not
+ * block on lock acquisition, except if stats updates have been pending for
+ * longer than PGSTAT_MAX_INTERVAL (60000ms).
+ *
+ * Whenever pending stats updates remain at the end of pgstat_report_stat() a
+ * suggested idle timeout is returned. Currently this is always
+ * PGSTAT_IDLE_INTERVAL (10000ms). Callers can use the returned time to set up
+ * a timeout after which to call pgstat_report_stat(true), but are not
+ * required to to do so.
  *
- * "disconnect" is "true" only for the last call before the backend
- * exits.  This makes sure that no data is lost and that interrupted
- * sessions are reported correctly.
+ * Note that this is called only when not within a transaction, so it is fair
+ * to use transaction stop time as an approximation of current time.
  */
-void
-pgstat_report_stat(bool disconnect)
+long
+pgstat_report_stat(bool force)
 {
-       static TimestampTz last_report = 0;
-
+       static TimestampTz pending_since = 0;
+       static TimestampTz last_flush = 0;
+       bool            partial_flush;
        TimestampTz now;
+       bool            nowait;
 
        pgstat_assert_is_up();
+       Assert(!IsTransactionBlock());
 
-       /*
-        * Don't expend a clock check if nothing to do.
-        */
-       if (!have_relation_stats &&
-               pgStatXactCommit == 0 && pgStatXactRollback == 0 &&
-               !pgstat_have_pending_wal() &&
-               !have_function_stats && !disconnect)
-               return;
+       /* Don't expend a clock check if nothing to do */
+       if (dlist_is_empty(&pgStatPending) &&
+               !have_slrustats &&
+               !pgstat_have_pending_wal())
+       {
+               Assert(pending_since == 0);
+               return 0;
+       }
 
        /*
-        * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
-        * msec since we last sent one, or the backend is about to exit.
+        * There should never be stats to report once stats are shut down. Can't
+        * assert that before the checks above, as there is an unconditional
+        * pgstat_report_stat() call in pgstat_shutdown_hook() - which at least
+        * the process that ran pgstat_before_server_shutdown() will still call.
         */
+       Assert(!pgStatLocal.shmem->is_shutdown);
+
        now = GetCurrentTransactionStopTimestamp();
-       if (!disconnect &&
-               !TimestampDifferenceExceeds(last_report, now, PGSTAT_STAT_INTERVAL))
-               return;
 
-       last_report = now;
+       if (!force)
+       {
+               if (pending_since > 0 &&
+                       TimestampDifferenceExceeds(pending_since, now, PGSTAT_MAX_INTERVAL))
+               {
+                       /* don't keep pending updates longer than PGSTAT_MAX_INTERVAL */
+                       force = true;
+               }
+               else if (last_flush > 0 &&
+                                !TimestampDifferenceExceeds(last_flush, now, PGSTAT_MIN_INTERVAL))
+               {
+                       /* don't flush too frequently */
+                       if (pending_since == 0)
+                               pending_since = now;
 
-       if (disconnect)
-               pgstat_report_disconnect(MyDatabaseId);
+                       return PGSTAT_IDLE_INTERVAL;
+               }
+       }
 
-       /* First, send relation statistics */
-       pgstat_send_tabstats(now, disconnect);
+       pgstat_update_dbstats(now);
 
-       /* Now, send function statistics */
-       pgstat_send_funcstats();
+       /* don't wait for lock acquisition when !force */
+       nowait = !force;
 
-       /* Send WAL statistics */
-       pgstat_report_wal(true);
+       partial_flush = false;
 
-       /* Finally send SLRU statistics */
-       pgstat_send_slru();
-}
+       /* flush database / relation / function / ... stats */
+       partial_flush |= pgstat_flush_pending_entries(nowait);
 
-/*
- * Will tell the collector about objects he can get rid of.
- */
-void
-pgstat_vacuum_stat(void)
-{
-       HTAB       *htab;
-       PgStat_MsgTabpurge msg;
-       PgStat_MsgFuncpurge f_msg;
-       HASH_SEQ_STATUS hstat;
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatTabEntry *tabentry;
-       PgStat_StatFuncEntry *funcentry;
-       int                     len;
-
-       if (pgStatSock == PGINVALID_SOCKET)
-               return;
+       /* flush wal stats */
+       partial_flush |= pgstat_flush_wal(nowait);
 
-       /*
-        * If not done for this transaction, read the statistics collector stats
-        * file into some hash tables.
-        */
-       backend_read_statsfile();
+       /* flush SLRU stats */
+       partial_flush |= pgstat_slru_flush(nowait);
 
-       /*
-        * Read pg_database and make a list of OIDs of all existing databases
-        */
-       htab = pgstat_collect_oids(DatabaseRelationId, Anum_pg_database_oid);
+       last_flush = now;
 
        /*
-        * Search the database hash table for dead databases and tell the
-        * collector to drop them.
+        * If some of the pending stats could not be flushed due to lock
+        * contention, let the caller know when to retry.
         */
-       hash_seq_init(&hstat, pgStatDBHash);
-       while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
+       if (partial_flush)
        {
-               Oid                     dbid = dbentry->databaseid;
-
-               CHECK_FOR_INTERRUPTS();
-
-               /* the DB entry for shared tables (with InvalidOid) is never dropped */
-               if (OidIsValid(dbid) &&
-                       hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
-                       pgstat_drop_database(dbid);
-       }
-
-       /* Clean up */
-       hash_destroy(htab);
+               /* force should have prevented us from getting here */
+               Assert(!force);
 
-       /*
-        * Search for all the dead replication slots in stats hashtable and tell
-        * the stats collector to drop them.
-        */
-       if (replSlotStatHash)
-       {
-               PgStat_StatReplSlotEntry *slotentry;
+               /* remember since when stats have been pending */
+               if (pending_since == 0)
+                       pending_since = now;
 
-               hash_seq_init(&hstat, replSlotStatHash);
-               while ((slotentry = (PgStat_StatReplSlotEntry *) hash_seq_search(&hstat)) != NULL)
-               {
-                       CHECK_FOR_INTERRUPTS();
-
-                       if (SearchNamedReplicationSlot(NameStr(slotentry->slotname), true) == NULL)
-                       {
-                               PgStat_MsgReplSlot msg;
-
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_REPLSLOT);
-                               namestrcpy(&msg.m_slotname, NameStr(slotentry->slotname));
-                               msg.m_create = false;
-                               msg.m_drop = true;
-                               pgstat_send(&msg, sizeof(PgStat_MsgReplSlot));
-                       }
-               }
+               return PGSTAT_IDLE_INTERVAL;
        }
 
-       /*
-        * Repeat the above steps for subscriptions, if subscription stats are
-        * being collected.
-        */
-       if (subscriptionStatHash)
-       {
-               PgStat_StatSubEntry *subentry;
+       pending_since = 0;
 
-               /*
-                * Read pg_subscription and make a list of OIDs of all existing
-                * subscriptions.
-                */
-               htab = pgstat_collect_oids(SubscriptionRelationId, Anum_pg_subscription_oid);
+       return 0;
+}
 
-               hash_seq_init(&hstat, subscriptionStatHash);
-               while ((subentry = (PgStat_StatSubEntry *) hash_seq_search(&hstat)) != NULL)
-               {
-                       CHECK_FOR_INTERRUPTS();
+/*
+ * Only for use by pgstat_reset_counters()
+ */
+static bool
+match_db_entries(PgStatShared_HashEntry *entry, Datum match_data)
+{
+       return entry->key.dboid == DatumGetObjectId(MyDatabaseId);
+}
 
-                       if (hash_search(htab, (void *) &(subentry->subid), HASH_FIND, NULL) == NULL)
-                               pgstat_drop_subscription(subentry->subid);
-               }
+/*
+ * Reset counters for our database.
+ *
+ * Permission checking for this function is managed through the normal
+ * GRANT system.
+ */
+void
+pgstat_reset_counters(void)
+{
+       TimestampTz ts = GetCurrentTimestamp();
 
-               hash_destroy(htab);
-       }
+       pgstat_reset_matching_entries(match_db_entries,
+                                                                 ObjectIdGetDatum(MyDatabaseId),
+                                                                 ts);
+}
 
-       /*
-        * Lookup our own database entry; if not found, nothing more to do.
-        */
-       dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                                                                (void *) &MyDatabaseId,
-                                                                                                HASH_FIND, NULL);
-       if (dbentry == NULL || dbentry->tables == NULL)
-               return;
+/*
+ * Reset a single variable-numbered entry.
+ *
+ * If the stats kind is within a database, also reset the database's
+ * stat_reset_timestamp.
+ *
+ * Permission checking for this function is managed through the normal
+ * GRANT system.
+ */
+void
+pgstat_reset(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+       const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+       TimestampTz ts = GetCurrentTimestamp();
 
-       /*
-        * Similarly to above, make a list of all known relations in this DB.
-        */
-       htab = pgstat_collect_oids(RelationRelationId, Anum_pg_class_oid);
+       /* not needed atm, and doesn't make sense with the current signature */
+       Assert(!pgstat_get_kind_info(kind)->fixed_amount);
 
-       /*
-        * Initialize our messages table counter to zero
-        */
-       msg.m_nentries = 0;
+       /* reset the "single counter" */
+       pgstat_reset_entry(kind, dboid, objoid, ts);
 
-       /*
-        * Check for all tables listed in stats hashtable if they still exist.
-        */
-       hash_seq_init(&hstat, dbentry->tables);
-       while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
-       {
-               Oid                     tabid = tabentry->tableid;
+       if (!kind_info->accessed_across_databases)
+               pgstat_reset_database_timestamp(dboid, ts);
+}
 
-               CHECK_FOR_INTERRUPTS();
+/*
+ * Reset stats for all entries of a kind.
+ *
+ * Permission checking for this function is managed through the normal
+ * GRANT system.
+ */
+void
+pgstat_reset_of_kind(PgStat_Kind kind)
+{
+       const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+       TimestampTz ts = GetCurrentTimestamp();
 
-               if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
-                       continue;
+       if (kind_info->fixed_amount)
+               kind_info->reset_all_cb(ts);
+       else
+               pgstat_reset_entries_of_kind(kind, ts);
+}
 
-               /*
-                * Not there, so add this table's Oid to the message
-                */
-               msg.m_tableid[msg.m_nentries++] = tabid;
 
-               /*
-                * If the message is full, send it out and reinitialize to empty
-                */
-               if (msg.m_nentries >= PGSTAT_NUM_TABPURGE)
-               {
-                       len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-                               + msg.m_nentries * sizeof(Oid);
+/* ------------------------------------------------------------
+ * Fetching of stats
+ * ------------------------------------------------------------
+ */
 
-                       pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-                       msg.m_databaseid = MyDatabaseId;
-                       pgstat_send(&msg, len);
+/*
+ * Discard any data collected in the current transaction.  Any subsequent
+ * request will cause new snapshots to be read.
+ *
+ * This is also invoked during transaction commit or abort to discard
+ * the no-longer-wanted snapshot.
+ */
+void
+pgstat_clear_snapshot(void)
+{
+       pgstat_assert_is_up();
 
-                       msg.m_nentries = 0;
-               }
-       }
+       memset(&pgStatLocal.snapshot.fixed_valid, 0,
+                  sizeof(pgStatLocal.snapshot.fixed_valid));
+       pgStatLocal.snapshot.stats = NULL;
+       pgStatLocal.snapshot.mode = PGSTAT_FETCH_CONSISTENCY_NONE;
 
-       /*
-        * Send the rest
-        */
-       if (msg.m_nentries > 0)
+       /* Release memory, if any was allocated */
+       if (pgStatLocal.snapshot.context)
        {
-               len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-                       + msg.m_nentries * sizeof(Oid);
+               MemoryContextDelete(pgStatLocal.snapshot.context);
 
-               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-               msg.m_databaseid = MyDatabaseId;
-               pgstat_send(&msg, len);
+               /* Reset variables */
+               pgStatLocal.snapshot.context = NULL;
        }
 
-       /* Clean up */
-       hash_destroy(htab);
-
        /*
-        * Now repeat the above steps for functions.  However, we needn't bother
-        * in the common case where no function stats are being collected.
+        * Historically the backend_status.c facilities lived in this file, and
+        * were reset with the same function. For now keep it that way, and
+        * forward the reset request.
         */
-       if (dbentry->functions != NULL &&
-               hash_get_num_entries(dbentry->functions) > 0)
-       {
-               htab = pgstat_collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
+       pgstat_clear_backend_activity_snapshot();
+}
 
-               pgstat_setheader(&f_msg.m_hdr, PGSTAT_MTYPE_FUNCPURGE);
-               f_msg.m_databaseid = MyDatabaseId;
-               f_msg.m_nentries = 0;
+void *
+pgstat_fetch_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+       PgStat_HashKey key;
+       PgStat_EntryRef *entry_ref;
+       void       *stats_data;
+       const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
-               hash_seq_init(&hstat, dbentry->functions);
-               while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&hstat)) != NULL)
-               {
-                       Oid                     funcid = funcentry->functionid;
+       /* should be called from backends */
+       Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
+       AssertArg(!kind_info->fixed_amount);
 
-                       CHECK_FOR_INTERRUPTS();
+       pgstat_prep_snapshot();
 
-                       if (hash_search(htab, (void *) &funcid, HASH_FIND, NULL) != NULL)
-                               continue;
+       key.kind = kind;
+       key.dboid = dboid;
+       key.objoid = objoid;
 
-                       /*
-                        * Not there, so add this function's Oid to the message
-                        */
-                       f_msg.m_functionid[f_msg.m_nentries++] = funcid;
+       /* if we need to build a full snapshot, do so */
+       if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT)
+               pgstat_build_snapshot();
 
-                       /*
-                        * If the message is full, send it out and reinitialize to empty
-                        */
-                       if (f_msg.m_nentries >= PGSTAT_NUM_FUNCPURGE)
-                       {
-                               len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-                                       + f_msg.m_nentries * sizeof(Oid);
+       /* if caching is desired, look up in cache */
+       if (pgstat_fetch_consistency > PGSTAT_FETCH_CONSISTENCY_NONE)
+       {
+               PgStat_SnapshotEntry *entry = NULL;
 
-                               pgstat_send(&f_msg, len);
+               entry = pgstat_snapshot_lookup(pgStatLocal.snapshot.stats, key);
 
-                               f_msg.m_nentries = 0;
-                       }
-               }
+               if (entry)
+                       return entry->data;
 
                /*
-                * Send the rest
+                * If we built a full snapshot and the key is not in
+                * pgStatLocal.snapshot.stats, there are no matching stats.
                 */
-               if (f_msg.m_nentries > 0)
-               {
-                       len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-                               + f_msg.m_nentries * sizeof(Oid);
+               if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT)
+                       return NULL;
+       }
 
-                       pgstat_send(&f_msg, len);
-               }
+       pgStatLocal.snapshot.mode = pgstat_fetch_consistency;
 
-               hash_destroy(htab);
-       }
-}
+       entry_ref = pgstat_get_entry_ref(kind, dboid, objoid, false, NULL);
 
-/*
- * Collect the OIDs of all objects listed in the specified system catalog
- * into a temporary hash table.  Caller should hash_destroy the result
- * when done with it.  (However, we make the table in CurrentMemoryContext
- * so that it will be freed properly in event of an error.)
- */
-static HTAB *
-pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
-{
-       HTAB       *htab;
-       HASHCTL         hash_ctl;
-       Relation        rel;
-       TableScanDesc scan;
-       HeapTuple       tup;
-       Snapshot        snapshot;
-
-       hash_ctl.keysize = sizeof(Oid);
-       hash_ctl.entrysize = sizeof(Oid);
-       hash_ctl.hcxt = CurrentMemoryContext;
-       htab = hash_create("Temporary table of OIDs",
-                                          PGSTAT_TAB_HASH_SIZE,
-                                          &hash_ctl,
-                                          HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-       rel = table_open(catalogid, AccessShareLock);
-       snapshot = RegisterSnapshot(GetLatestSnapshot());
-       scan = table_beginscan(rel, snapshot, 0, NULL);
-       while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
+       if (entry_ref == NULL || entry_ref->shared_entry->dropped)
        {
-               Oid                     thisoid;
-               bool            isnull;
+               /* create empty entry when using PGSTAT_FETCH_CONSISTENCY_CACHE */
+               if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_CACHE)
+               {
+                       PgStat_SnapshotEntry *entry = NULL;
+                       bool            found;
 
-               thisoid = heap_getattr(tup, anum_oid, RelationGetDescr(rel), &isnull);
-               Assert(!isnull);
+                       entry = pgstat_snapshot_insert(pgStatLocal.snapshot.stats, key, &found);
+                       Assert(!found);
+                       entry->data = NULL;
+               }
+               return NULL;
+       }
 
-               CHECK_FOR_INTERRUPTS();
+       /*
+        * Allocate in caller's context for PGSTAT_FETCH_CONSISTENCY_NONE,
+        * otherwise we could quickly end up with a fair bit of memory used due to
+        * repeated accesses.
+        */
+       if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_NONE)
+               stats_data = palloc(kind_info->shared_data_len);
+       else
+               stats_data = MemoryContextAlloc(pgStatLocal.snapshot.context,
+                                                                               kind_info->shared_data_len);
+       memcpy(stats_data,
+                  pgstat_get_entry_data(kind, entry_ref->shared_stats),
+                  kind_info->shared_data_len);
+
+       if (pgstat_fetch_consistency > PGSTAT_FETCH_CONSISTENCY_NONE)
+       {
+               PgStat_SnapshotEntry *entry = NULL;
+               bool            found;
 
-               (void) hash_search(htab, (void *) &thisoid, HASH_ENTER, NULL);
+               entry = pgstat_snapshot_insert(pgStatLocal.snapshot.stats, key, &found);
+               entry->data = stats_data;
        }
-       table_endscan(scan);
-       UnregisterSnapshot(snapshot);
-       table_close(rel, AccessShareLock);
 
-       return htab;
+       return stats_data;
 }
 
 /*
- * Reset counters for our database.
- *
- * Permission checking for this function is managed through the normal
- * GRANT system.
+ * If a stats snapshot has been taken, return the timestamp at which that was
+ * done, and set *have_snapshot to true. Otherwise *have_snapshot is set to
+ * false.
  */
-void
-pgstat_reset_counters(void)
+TimestampTz
+pgstat_get_stat_snapshot_timestamp(bool *have_snapshot)
 {
-       PgStat_MsgResetcounter msg;
+       if (pgStatLocal.snapshot.mode == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT)
+       {
+               *have_snapshot = true;
+               return pgStatLocal.snapshot.snapshot_timestamp;
+       }
 
-       if (pgStatSock == PGINVALID_SOCKET)
-               return;
+       *have_snapshot = false;
 
-       pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETCOUNTER);
-       msg.m_databaseid = MyDatabaseId;
-       pgstat_send(&msg, sizeof(msg));
+       return 0;
 }
 
 /*
- * Reset a single variable-numbered entry.
- *
- * If the stats kind is within a database, also reset the database's
- * stat_reset_timestamp.
+ * Ensure snapshot for fixed-numbered 'kind' exists.
  *
- * Permission checking for this function is managed through the normal
- * GRANT system.
+ * Typically used by the pgstat_fetch_* functions for a kind of stats, before
+ * massaging the data into the desired format.
  */
 void
-pgstat_reset(PgStat_Kind kind, Oid dboid, Oid objoid)
+pgstat_snapshot_fixed(PgStat_Kind kind)
 {
+       AssertArg(pgstat_is_kind_valid(kind));
+       AssertArg(pgstat_get_kind_info(kind)->fixed_amount);
 
-       if (pgStatSock == PGINVALID_SOCKET)
-               return;
+       if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT)
+               pgstat_build_snapshot();
+       else
+               pgstat_build_snapshot_fixed(kind);
 
-       switch (kind)
-       {
-               case PGSTAT_KIND_FUNCTION:
-               case PGSTAT_KIND_RELATION:
-                       {
-                               PgStat_MsgResetsinglecounter msg;
-
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSINGLECOUNTER);
-                               msg.m_databaseid = dboid;
-                               msg.m_resettype = kind;
-                               msg.m_objectid = objoid;
-                               pgstat_send(&msg, sizeof(msg));
-                       }
-                       break;
-
-               case PGSTAT_KIND_SUBSCRIPTION:
-                       {
-                               PgStat_MsgResetsubcounter msg;
-
-                               Assert(dboid == InvalidOid);
-                               msg.m_subid = objoid;
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSUBCOUNTER);
-                       }
-                       break;
-
-               default:
-                       elog(ERROR, "unexpected");
-       }
+       Assert(pgStatLocal.snapshot.fixed_valid[kind]);
 }
 
-/*
- * Reset stats for all entries of a kind.
- *
- * Permission checking for this function is managed through the normal
- * GRANT system.
- */
-void
-pgstat_reset_of_kind(PgStat_Kind kind)
+static void
+pgstat_prep_snapshot(void)
 {
-       if (pgStatSock == PGINVALID_SOCKET)
+       if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_NONE ||
+               pgStatLocal.snapshot.stats != NULL)
                return;
 
-       switch (kind)
-       {
-               case PGSTAT_KIND_ARCHIVER:
-               case PGSTAT_KIND_BGWRITER:
-               case PGSTAT_KIND_CHECKPOINTER:
-               case PGSTAT_KIND_WAL:
-                       {
-                               PgStat_MsgResetsharedcounter msg;
-
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
-                               msg.m_resettarget = kind;
-                               pgstat_send(&msg, sizeof(msg));
-                       }
-                       break;
-               case PGSTAT_KIND_SLRU:
-                       {
-                               PgStat_MsgResetslrucounter msg;
-
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSLRUCOUNTER);
-                               msg.m_index = -1;
-                               pgstat_send(&msg, sizeof(msg));
-                       }
-                       break;
-               case PGSTAT_KIND_REPLSLOT:
-                       {
-                               PgStat_MsgResetreplslotcounter msg;
-
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETREPLSLOTCOUNTER);
-                               msg.clearall = true;
-                               pgstat_send(&msg, sizeof(msg));
-                       }
-                       break;
-
-               case PGSTAT_KIND_SUBSCRIPTION:
-                       {
-                               PgStat_MsgResetsubcounter msg;
-
-                               msg.m_subid = InvalidOid;
-                               pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSUBCOUNTER);
-
-                               pgstat_send(&msg, sizeof(msg));
-                       }
-                       break;
-
-               default:
-                       elog(ERROR, "unexpected");
-       }
-}
-
-/*
- * Send some junk data to the collector to increase traffic.
- */
-void
-pgstat_ping(void)
-{
-       PgStat_MsgDummy msg;
-
-       if (pgStatSock == PGINVALID_SOCKET)
-               return;
+       if (!pgStatLocal.snapshot.context)
+               pgStatLocal.snapshot.context = AllocSetContextCreate(TopMemoryContext,
+                                                                                                                        "PgStat Snapshot",
+                                                                                                                        ALLOCSET_SMALL_SIZES);
 
-       pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DUMMY);
-       pgstat_send(&msg, sizeof(msg));
+       pgStatLocal.snapshot.stats =
+               pgstat_snapshot_create(pgStatLocal.snapshot.context,
+                                                          PGSTAT_SNAPSHOT_HASH_SIZE,
+                                                          NULL);
 }
 
-/*
- * Notify collector that we need fresh data.
- */
 static void
-pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time, Oid databaseid)
+pgstat_build_snapshot(void)
 {
-       PgStat_MsgInquiry msg;
+       dshash_seq_status hstat;
+       PgStatShared_HashEntry *p;
 
-       pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
-       msg.clock_time = clock_time;
-       msg.cutoff_time = cutoff_time;
-       msg.databaseid = databaseid;
-       pgstat_send(&msg, sizeof(msg));
-}
+       /* should only be called when we need a snapshot */
+       Assert(pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT);
 
-/*
- * Discard any data collected in the current transaction.  Any subsequent
- * request will cause new snapshots to be read.
- *
- * This is also invoked during transaction commit or abort to discard
- * the no-longer-wanted snapshot.
- */
-void
-pgstat_clear_snapshot(void)
-{
-       pgstat_assert_is_up();
+       /* snapshot already built */
+       if (pgStatLocal.snapshot.mode == PGSTAT_FETCH_CONSISTENCY_SNAPSHOT)
+               return;
 
-       /* Release memory, if any was allocated */
-       if (pgStatLocalContext)
-               MemoryContextDelete(pgStatLocalContext);
+       pgstat_prep_snapshot();
 
-       /* Reset variables */
-       pgStatLocalContext = NULL;
-       pgStatDBHash = NULL;
-       replSlotStatHash = NULL;
-       subscriptionStatHash = NULL;
+       Assert(pgStatLocal.snapshot.stats->members == 0);
 
-       /*
-        * Historically the backend_status.c facilities lived in this file, and
-        * were reset with the same function. For now keep it that way, and
-        * forward the reset request.
-        */
-       pgstat_clear_backend_activity_snapshot();
-}
+       pgStatLocal.snapshot.snapshot_timestamp = GetCurrentTimestamp();
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * the collected statistics for one database or NULL. NULL doesn't mean
- * that the database doesn't exist, just that there are no statistics, so the
- * caller is better off to report ZERO instead.
- */
-PgStat_StatDBEntry *
-pgstat_fetch_stat_dbentry(Oid dbid)
-{
        /*
-        * If not done for this transaction, read the statistics collector stats
-        * file into some hash tables.
+        * Snapshot all variable stats.
         */
-       backend_read_statsfile();
+       dshash_seq_init(&hstat, pgStatLocal.shared_hash, false);
+       while ((p = dshash_seq_next(&hstat)) != NULL)
+       {
+               PgStat_Kind kind = p->key.kind;
+               const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+               bool            found;
+               PgStat_SnapshotEntry *entry;
+               PgStatShared_Common *stats_data;
+
+               /*
+                * Check if the stats object should be included in the snapshot.
+                * Unless the stats kind can be accessed from all databases (e.g.,
+                * database stats themselves), we only include stats for the current
+                * database or objects not associated with a database (e.g. shared
+                * relations).
+                */
+               if (p->key.dboid != MyDatabaseId &&
+                       p->key.dboid != InvalidOid &&
+                       !kind_info->accessed_across_databases)
+                       continue;
+
+               if (p->dropped)
+                       continue;
+
+               Assert(pg_atomic_read_u32(&p->refcount) > 0);
+
+               stats_data = dsa_get_address(pgStatLocal.dsa, p->body);
+               Assert(stats_data);
+
+               entry = pgstat_snapshot_insert(pgStatLocal.snapshot.stats, p->key, &found);
+               Assert(!found);
+
+               entry->data = MemoryContextAlloc(pgStatLocal.snapshot.context,
+                                                                                kind_info->shared_size);
+               memcpy(entry->data,
+                          pgstat_get_entry_data(kind, stats_data),
+                          kind_info->shared_size);
+       }
+       dshash_seq_term(&hstat);
 
        /*
-        * Lookup the requested database; return NULL if not found
+        * Build snapshot of all fixed-numbered stats.
         */
-       return (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                                                         (void *) &dbid,
-                                                                                         HASH_FIND, NULL);
-}
+       for (int kind = PGSTAT_KIND_FIRST_VALID; kind <= PGSTAT_KIND_LAST; kind++)
+       {
+               const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the global statistics struct.
- */
-PgStat_GlobalStats *
-pgstat_fetch_global(void)
-{
-       backend_read_statsfile();
+               if (!kind_info->fixed_amount)
+               {
+                       Assert(kind_info->snapshot_cb == NULL);
+                       continue;
+               }
+
+               pgstat_build_snapshot_fixed(kind);
+       }
 
-       return &globalStats;
+       pgStatLocal.snapshot.mode = PGSTAT_FETCH_CONSISTENCY_SNAPSHOT;
 }
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * the collected statistics for one table or NULL. NULL doesn't mean
- * that the table doesn't exist, just that there are no statistics, so the
- * caller is better off to report ZERO instead.
- */
-PgStat_StatTabEntry *
-pgstat_fetch_stat_tabentry(Oid relid)
+static void
+pgstat_build_snapshot_fixed(PgStat_Kind kind)
 {
-       Oid                     dbid;
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatTabEntry *tabentry;
+       const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
-       /*
-        * If not done for this transaction, read the statistics collector stats
-        * file into some hash tables.
-        */
-       backend_read_statsfile();
+       Assert(kind_info->fixed_amount);
+       Assert(kind_info->snapshot_cb != NULL);
 
-       /*
-        * Lookup our database, then look in its table hash table.
-        */
-       dbid = MyDatabaseId;
-       dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                                                                (void *) &dbid,
-                                                                                                HASH_FIND, NULL);
-       if (dbentry != NULL && dbentry->tables != NULL)
+       if (pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_NONE)
        {
-               tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                                                                          (void *) &relid,
-                                                                                                          HASH_FIND, NULL);
-               if (tabentry)
-                       return tabentry;
+               /* rebuild every time */
+               pgStatLocal.snapshot.fixed_valid[kind] = false;
        }
-
-       /*
-        * If we didn't find it, maybe it's a shared table.
-        */
-       dbid = InvalidOid;
-       dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                                                                (void *) &dbid,
-                                                                                                HASH_FIND, NULL);
-       if (dbentry != NULL && dbentry->tables != NULL)
+       else if (pgStatLocal.snapshot.fixed_valid[kind])
        {
-               tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                                                                          (void *) &relid,
-                                                                                                          HASH_FIND, NULL);
-               if (tabentry)
-                       return tabentry;
+               /* in snapshot mode we shouldn't get called again */
+               Assert(pgstat_fetch_consistency == PGSTAT_FETCH_CONSISTENCY_CACHE);
+               return;
        }
 
-       return NULL;
+       Assert(!pgStatLocal.snapshot.fixed_valid[kind]);
+
+       kind_info->snapshot_cb();
+
+       Assert(!pgStatLocal.snapshot.fixed_valid[kind]);
+       pgStatLocal.snapshot.fixed_valid[kind] = true;
 }
 
 
+/* ------------------------------------------------------------
+ * Backend-local pending stats infrastructure
+ * ------------------------------------------------------------
+ */
+
 /*
- * Support function for the SQL-callable pgstat* functions. Returns
- * the collected statistics for one function or NULL.
+ * Returns the appropriate PgStat_EntryRef, preparing it to receive pending
+ * stats if not already done.
+ *
+ * If created_entry is non-NULL, it'll be set to true if the entry is newly
+ * created, false otherwise.
  */
-PgStat_StatFuncEntry *
-pgstat_fetch_stat_funcentry(Oid func_id)
+PgStat_EntryRef *
+pgstat_prep_pending_entry(PgStat_Kind kind, Oid dboid, Oid objoid, bool *created_entry)
 {
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatFuncEntry *funcentry = NULL;
+       PgStat_EntryRef *entry_ref;
 
-       /* load the stats file if needed */
-       backend_read_statsfile();
+       /* need to be able to flush out */
+       Assert(pgstat_get_kind_info(kind)->flush_pending_cb != NULL);
 
-       /* Lookup our database, then find the requested function.  */
-       dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-       if (dbentry != NULL && dbentry->functions != NULL)
+       if (unlikely(!pgStatPendingContext))
        {
-               funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-                                                                                                                (void *) &func_id,
-                                                                                                                HASH_FIND, NULL);
+               pgStatPendingContext =
+                       AllocSetContextCreate(CacheMemoryContext,
+                                                                 "PgStat Pending",
+                                                                 ALLOCSET_SMALL_SIZES);
        }
 
-       return funcentry;
-}
+       entry_ref = pgstat_get_entry_ref(kind, dboid, objoid,
+                                                                        true, created_entry);
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the archiver statistics struct.
- */
-PgStat_ArchiverStats *
-pgstat_fetch_stat_archiver(void)
-{
-       backend_read_statsfile();
+       if (entry_ref->pending == NULL)
+       {
+               size_t          entrysize = pgstat_get_kind_info(kind)->pending_size;
 
-       return &archiverStats;
-}
+               Assert(entrysize != (size_t) -1);
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the bgwriter statistics struct.
- */
-PgStat_BgWriterStats *
-pgstat_fetch_stat_bgwriter(void)
-{
-       backend_read_statsfile();
+               entry_ref->pending = MemoryContextAllocZero(pgStatPendingContext, entrysize);
+               dlist_push_tail(&pgStatPending, &entry_ref->pending_node);
+       }
 
-       return &globalStats.bgwriter;
+       return entry_ref;
 }
 
 /*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the checkpointer statistics struct.
+ * Return an existing stats entry, or NULL.
+ *
+ * This should only be used for helper function for pgstatfuncs.c - outside of
+ * that it shouldn't be needed.
  */
-PgStat_CheckpointerStats *
-pgstat_fetch_stat_checkpointer(void)
+PgStat_EntryRef *
+pgstat_fetch_pending_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
 {
-       backend_read_statsfile();
+       PgStat_EntryRef *entry_ref;
 
-       return &globalStats.checkpointer;
-}
+       entry_ref = pgstat_get_entry_ref(kind, dboid, objoid, false, NULL);
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the WAL statistics struct.
- */
-PgStat_WalStats *
-pgstat_fetch_stat_wal(void)
-{
-       backend_read_statsfile();
+       if (entry_ref == NULL || entry_ref->pending == NULL)
+               return NULL;
 
-       return &walStats;
+       return entry_ref;
 }
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the slru statistics struct.
- */
-PgStat_SLRUStats *
-pgstat_fetch_slru(void)
+void
+pgstat_delete_pending_entry(PgStat_EntryRef *entry_ref)
 {
-       backend_read_statsfile();
+       PgStat_Kind kind = entry_ref->shared_entry->key.kind;
+       const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+       void       *pending_data = entry_ref->pending;
 
-       return slruStats;
-}
+       Assert(pending_data != NULL);
+       /* !fixed_amount stats should be handled explicitly */
+       Assert(!pgstat_get_kind_info(kind)->fixed_amount);
 
-/*
- * Support function for the SQL-callable pgstat* functions. Returns
- * a pointer to the replication slot statistics struct.
- */
-PgStat_StatReplSlotEntry *
-pgstat_fetch_replslot(NameData slotname)
-{
-       backend_read_statsfile();
+       if (kind_info->delete_pending_cb)
+               kind_info->delete_pending_cb(entry_ref);
+
+       pfree(pending_data);
+       entry_ref->pending = NULL;
 
-       return pgstat_get_replslot_entry(slotname, false);
+       dlist_delete(&entry_ref->pending_node);
 }
 
 /*
- * Support function for the SQL-callable pgstat* functions. Returns
- * the collected statistics for one subscription or NULL.
+ * Flush out pending stats for database objects (databases, relations,
+ * functions).
  */
-PgStat_StatSubEntry *
-pgstat_fetch_stat_subscription(Oid subid)
+static bool
+pgstat_flush_pending_entries(bool nowait)
 {
-       /* Load the stats file if needed */
-       backend_read_statsfile();
+       bool            have_pending = false;
+       dlist_node *cur = NULL;
+
+       /*
+        * Need to be a bit careful iterating over the list of pending entries.
+        * Processing a pending entry may queue further pending entries to the end
+        * of the list that we want to process, so a simple iteration won't do.
+        * Further complicating matters is that we want to delete the current
+        * entry in each iteration from the list if we flushed successfully.
+        *
+        * So we just keep track of the next pointer in each loop iteration.
+        */
+       if (!dlist_is_empty(&pgStatPending))
+               cur = dlist_head_node(&pgStatPending);
+
+       while (cur)
+       {
+               PgStat_EntryRef *entry_ref =
+               dlist_container(PgStat_EntryRef, pending_node, cur);
+               PgStat_HashKey key = entry_ref->shared_entry->key;
+               PgStat_Kind kind = key.kind;
+               const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
+               bool            did_flush;
+               dlist_node *next;
+
+               Assert(!kind_info->fixed_amount);
+               Assert(kind_info->flush_pending_cb != NULL);
+
+               /* flush the stats, if possible */
+               did_flush = kind_info->flush_pending_cb(entry_ref, nowait);
+
+               Assert(did_flush || nowait);
 
-       return pgstat_get_subscription_entry(subid, false);
+               /* determine next entry, before deleting the pending entry */
+               if (dlist_has_next(&pgStatPending, cur))
+                       next = dlist_next_node(&pgStatPending, cur);
+               else
+                       next = NULL;
+
+               /* if successfully flushed, remove entry */
+               if (did_flush)
+                       pgstat_delete_pending_entry(entry_ref);
+               else
+                       have_pending = true;
+
+               cur = next;
+       }
+
+       Assert(dlist_is_empty(&pgStatPending) == !have_pending);
+
+       return have_pending;
 }
 
 
@@ -1464,16 +1156,33 @@ pgstat_fetch_stat_subscription(Oid subid)
  * ------------------------------------------------------------
  */
 
-/*
- * Create pgStatLocalContext, if not already done.
- */
-static void
-pgstat_setup_memcxt(void)
+PgStat_Kind
+pgstat_get_kind_from_str(char *kind_str)
+{
+       for (int kind = PGSTAT_KIND_FIRST_VALID; kind <= PGSTAT_KIND_LAST; kind++)
+       {
+               if (pg_strcasecmp(kind_str, pgstat_kind_infos[kind].name) == 0)
+                       return kind;
+       }
+
+       ereport(ERROR,
+                       (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                        errmsg("invalid statistics kind: \"%s\"", kind_str)));
+       return PGSTAT_KIND_DATABASE;    /* avoid compiler warnings */
+}
+
+static inline bool
+pgstat_is_kind_valid(int ikind)
 {
-       if (!pgStatLocalContext)
-               pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
-                                                                                                  "Statistics snapshot",
-                                                                                                  ALLOCSET_SMALL_SIZES);
+       return ikind >= PGSTAT_KIND_FIRST_VALID && ikind <= PGSTAT_KIND_LAST;
+}
+
+const PgStat_KindInfo *
+pgstat_get_kind_info(PgStat_Kind kind)
+{
+       AssertArg(pgstat_is_kind_valid(kind));
+
+       return &pgstat_kind_infos[kind];
 }
 
 /*
@@ -1489,642 +1198,44 @@ pgstat_assert_is_up(void)
 }
 #endif
 
-/*
- * Set common header fields in a statistics message
- */
-void
-pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
-{
-       hdr->m_type = mtype;
-}
-
-
-/*
- * Send out one statistics message to the collector
- */
-void
-pgstat_send(void *msg, int len)
-{
-       int                     rc;
-
-       pgstat_assert_is_up();
-
-       if (pgStatSock == PGINVALID_SOCKET)
-               return;
-
-       ((PgStat_MsgHdr *) msg)->m_size = len;
-
-       /* We'll retry after EINTR, but ignore all other failures */
-       do
-       {
-               rc = send(pgStatSock, msg, len, 0);
-       } while (rc < 0 && errno == EINTR);
-
-#ifdef USE_ASSERT_CHECKING
-       /* In debug builds, log send failures ... */
-       if (rc < 0)
-               elog(LOG, "could not send to statistics collector: %m");
-#endif
-}
-
-/*
- * Start up the statistics collector process.  This is the body of the
- * postmaster child process.
- *
- * The argc/argv parameters are valid only in EXEC_BACKEND case.
- */
-NON_EXEC_STATIC void
-PgstatCollectorMain(int argc, char *argv[])
-{
-       int                     len;
-       PgStat_Msg      msg;
-       int                     wr;
-       WaitEvent       event;
-       WaitEventSet *wes;
-
-       /*
-        * Ignore all signals usually bound to some action in the postmaster,
-        * except SIGHUP and SIGQUIT.  Note we don't need a SIGUSR1 handler to
-        * support latch operations, because we only use a local latch.
-        */
-       pqsignal(SIGHUP, SignalHandlerForConfigReload);
-       pqsignal(SIGINT, SIG_IGN);
-       pqsignal(SIGTERM, SIG_IGN);
-       pqsignal(SIGQUIT, SignalHandlerForShutdownRequest);
-       pqsignal(SIGALRM, SIG_IGN);
-       pqsignal(SIGPIPE, SIG_IGN);
-       pqsignal(SIGUSR1, SIG_IGN);
-       pqsignal(SIGUSR2, SIG_IGN);
-       /* Reset some signals that are accepted by postmaster but not here */
-       pqsignal(SIGCHLD, SIG_DFL);
-       PG_SETMASK(&UnBlockSig);
-
-       MyBackendType = B_STATS_COLLECTOR;
-       init_ps_display(NULL);
-
-       /*
-        * Read in existing stats files or initialize the stats to zero.
-        */
-       pgStatRunningInCollector = true;
-       pgStatDBHash = pgstat_read_statsfiles(InvalidOid, true, true);
-
-       /* Prepare to wait for our latch or data in our socket. */
-       wes = CreateWaitEventSet(CurrentMemoryContext, 3);
-       AddWaitEventToSet(wes, WL_LATCH_SET, PGINVALID_SOCKET, MyLatch, NULL);
-       AddWaitEventToSet(wes, WL_POSTMASTER_DEATH, PGINVALID_SOCKET, NULL, NULL);
-       AddWaitEventToSet(wes, WL_SOCKET_READABLE, pgStatSock, NULL, NULL);
-
-       /*
-        * Loop to process messages until we get SIGQUIT or detect ungraceful
-        * death of our parent postmaster.
-        *
-        * For performance reasons, we don't want to do ResetLatch/WaitLatch after
-        * every message; instead, do that only after a recv() fails to obtain a
-        * message.  (This effectively means that if backends are sending us stuff
-        * like mad, we won't notice postmaster death until things slack off a
-        * bit; which seems fine.)      To do that, we have an inner loop that
-        * iterates as long as recv() succeeds.  We do check ConfigReloadPending
-        * inside the inner loop, which means that such interrupts will get
-        * serviced but the latch won't get cleared until next time there is a
-        * break in the action.
-        */
-       for (;;)
-       {
-               /* Clear any already-pending wakeups */
-               ResetLatch(MyLatch);
-
-               /*
-                * Quit if we get SIGQUIT from the postmaster.
-                */
-               if (ShutdownRequestPending)
-                       break;
-
-               /*
-                * Inner loop iterates as long as we keep getting messages, or until
-                * ShutdownRequestPending becomes set.
-                */
-               while (!ShutdownRequestPending)
-               {
-                       /*
-                        * Reload configuration if we got SIGHUP from the postmaster.
-                        */
-                       if (ConfigReloadPending)
-                       {
-                               ConfigReloadPending = false;
-                               ProcessConfigFile(PGC_SIGHUP);
-                       }
-
-                       /*
-                        * Write the stats file(s) if a new request has arrived that is
-                        * not satisfied by existing file(s).
-                        */
-                       if (pgstat_write_statsfile_needed())
-                               pgstat_write_statsfiles(false, false);
-
-                       /*
-                        * Try to receive and process a message.  This will not block,
-                        * since the socket is set to non-blocking mode.
-                        *
-                        * XXX On Windows, we have to force pgwin32_recv to cooperate,
-                        * despite the previous use of pg_set_noblock() on the socket.
-                        * This is extremely broken and should be fixed someday.
-                        */
-#ifdef WIN32
-                       pgwin32_noblock = 1;
-#endif
-
-                       len = recv(pgStatSock, (char *) &msg,
-                                          sizeof(PgStat_Msg), 0);
-
-#ifdef WIN32
-                       pgwin32_noblock = 0;
-#endif
-
-                       if (len < 0)
-                       {
-                               if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
-                                       break;          /* out of inner loop */
-                               ereport(ERROR,
-                                               (errcode_for_socket_access(),
-                                                errmsg("could not read statistics message: %m")));
-                       }
-
-                       /*
-                        * We ignore messages that are smaller than our common header
-                        */
-                       if (len < sizeof(PgStat_MsgHdr))
-                               continue;
-
-                       /*
-                        * The received length must match the length in the header
-                        */
-                       if (msg.msg_hdr.m_size != len)
-                               continue;
-
-                       /*
-                        * O.K. - we accept this message.  Process it.
-                        */
-                       switch (msg.msg_hdr.m_type)
-                       {
-                               case PGSTAT_MTYPE_DUMMY:
-                                       break;
-
-                               case PGSTAT_MTYPE_INQUIRY:
-                                       pgstat_recv_inquiry(&msg.msg_inquiry, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_TABSTAT:
-                                       pgstat_recv_tabstat(&msg.msg_tabstat, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_TABPURGE:
-                                       pgstat_recv_tabpurge(&msg.msg_tabpurge, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_DROPDB:
-                                       pgstat_recv_dropdb(&msg.msg_dropdb, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETCOUNTER:
-                                       pgstat_recv_resetcounter(&msg.msg_resetcounter, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETSHAREDCOUNTER:
-                                       pgstat_recv_resetsharedcounter(&msg.msg_resetsharedcounter,
-                                                                                                  len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETSINGLECOUNTER:
-                                       pgstat_recv_resetsinglecounter(&msg.msg_resetsinglecounter,
-                                                                                                  len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETSLRUCOUNTER:
-                                       pgstat_recv_resetslrucounter(&msg.msg_resetslrucounter,
-                                                                                                len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETREPLSLOTCOUNTER:
-                                       pgstat_recv_resetreplslotcounter(&msg.msg_resetreplslotcounter,
-                                                                                                        len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RESETSUBCOUNTER:
-                                       pgstat_recv_resetsubcounter(&msg.msg_resetsubcounter, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_AUTOVAC_START:
-                                       pgstat_recv_autovac(&msg.msg_autovacuum_start, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_VACUUM:
-                                       pgstat_recv_vacuum(&msg.msg_vacuum, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_ANALYZE:
-                                       pgstat_recv_analyze(&msg.msg_analyze, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_ARCHIVER:
-                                       pgstat_recv_archiver(&msg.msg_archiver, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_BGWRITER:
-                                       pgstat_recv_bgwriter(&msg.msg_bgwriter, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_CHECKPOINTER:
-                                       pgstat_recv_checkpointer(&msg.msg_checkpointer, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_WAL:
-                                       pgstat_recv_wal(&msg.msg_wal, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_SLRU:
-                                       pgstat_recv_slru(&msg.msg_slru, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_FUNCSTAT:
-                                       pgstat_recv_funcstat(&msg.msg_funcstat, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_FUNCPURGE:
-                                       pgstat_recv_funcpurge(&msg.msg_funcpurge, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_RECOVERYCONFLICT:
-                                       pgstat_recv_recoveryconflict(&msg.msg_recoveryconflict,
-                                                                                                len);
-                                       break;
-
-                               case PGSTAT_MTYPE_DEADLOCK:
-                                       pgstat_recv_deadlock(&msg.msg_deadlock, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_TEMPFILE:
-                                       pgstat_recv_tempfile(&msg.msg_tempfile, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_CHECKSUMFAILURE:
-                                       pgstat_recv_checksum_failure(&msg.msg_checksumfailure,
-                                                                                                len);
-                                       break;
-
-                               case PGSTAT_MTYPE_REPLSLOT:
-                                       pgstat_recv_replslot(&msg.msg_replslot, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_CONNECT:
-                                       pgstat_recv_connect(&msg.msg_connect, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_DISCONNECT:
-                                       pgstat_recv_disconnect(&msg.msg_disconnect, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_SUBSCRIPTIONDROP:
-                                       pgstat_recv_subscription_drop(&msg.msg_subscriptiondrop, len);
-                                       break;
-
-                               case PGSTAT_MTYPE_SUBSCRIPTIONERROR:
-                                       pgstat_recv_subscription_error(&msg.msg_subscriptionerror, len);
-                                       break;
-
-                               default:
-                                       break;
-                       }
-               }                                               /* end of inner message-processing loop */
-
-               /* Sleep until there's something to do */
-#ifndef WIN32
-               wr = WaitEventSetWait(wes, -1L, &event, 1, WAIT_EVENT_PGSTAT_MAIN);
-#else
-
-               /*
-                * Windows, at least in its Windows Server 2003 R2 incarnation,
-                * sometimes loses FD_READ events.  Waking up and retrying the recv()
-                * fixes that, so don't sleep indefinitely.  This is a crock of the
-                * first water, but until somebody wants to debug exactly what's
-                * happening there, this is the best we can do.  The two-second
-                * timeout matches our pre-9.2 behavior, and needs to be short enough
-                * to not provoke "using stale statistics" complaints from
-                * backend_read_statsfile.
-                */
-               wr = WaitEventSetWait(wes, 2 * 1000L /* msec */ , &event, 1,
-                                                         WAIT_EVENT_PGSTAT_MAIN);
-#endif
-
-               /*
-                * Emergency bailout if postmaster has died.  This is to avoid the
-                * necessity for manual cleanup of all postmaster children.
-                */
-               if (wr == 1 && event.events == WL_POSTMASTER_DEATH)
-                       break;
-       }                                                       /* end of outer loop */
-
-       /*
-        * Save the final stats to reuse at next startup.
-        */
-       pgstat_write_statsfiles(true, true);
-
-       FreeWaitEventSet(wes);
-
-       exit(0);
-}
-
-/*
- * Subroutine to clear stats in a database entry
- *
- * Tables and functions hashes are initialized to empty.
- */
-static void
-reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
-{
-       HASHCTL         hash_ctl;
-
-       dbentry->n_xact_commit = 0;
-       dbentry->n_xact_rollback = 0;
-       dbentry->n_blocks_fetched = 0;
-       dbentry->n_blocks_hit = 0;
-       dbentry->n_tuples_returned = 0;
-       dbentry->n_tuples_fetched = 0;
-       dbentry->n_tuples_inserted = 0;
-       dbentry->n_tuples_updated = 0;
-       dbentry->n_tuples_deleted = 0;
-       dbentry->last_autovac_time = 0;
-       dbentry->n_conflict_tablespace = 0;
-       dbentry->n_conflict_lock = 0;
-       dbentry->n_conflict_snapshot = 0;
-       dbentry->n_conflict_bufferpin = 0;
-       dbentry->n_conflict_startup_deadlock = 0;
-       dbentry->n_temp_files = 0;
-       dbentry->n_temp_bytes = 0;
-       dbentry->n_deadlocks = 0;
-       dbentry->n_checksum_failures = 0;
-       dbentry->last_checksum_failure = 0;
-       dbentry->n_block_read_time = 0;
-       dbentry->n_block_write_time = 0;
-       dbentry->n_sessions = 0;
-       dbentry->total_session_time = 0;
-       dbentry->total_active_time = 0;
-       dbentry->total_idle_in_xact_time = 0;
-       dbentry->n_sessions_abandoned = 0;
-       dbentry->n_sessions_fatal = 0;
-       dbentry->n_sessions_killed = 0;
-
-       dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-       dbentry->stats_timestamp = 0;
-
-       hash_ctl.keysize = sizeof(Oid);
-       hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-       dbentry->tables = hash_create("Per-database table",
-                                                                 PGSTAT_TAB_HASH_SIZE,
-                                                                 &hash_ctl,
-                                                                 HASH_ELEM | HASH_BLOBS);
-
-       hash_ctl.keysize = sizeof(Oid);
-       hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-       dbentry->functions = hash_create("Per-database function",
-                                                                        PGSTAT_FUNCTION_HASH_SIZE,
-                                                                        &hash_ctl,
-                                                                        HASH_ELEM | HASH_BLOBS);
-}
-
-/*
- * Lookup the hash table entry for the specified database. If no hash
- * table entry exists, initialize it, if the create parameter is true.
- * Else, return NULL.
- */
-static PgStat_StatDBEntry *
-pgstat_get_db_entry(Oid databaseid, bool create)
-{
-       PgStat_StatDBEntry *result;
-       bool            found;
-       HASHACTION      action = (create ? HASH_ENTER : HASH_FIND);
-
-       /* Lookup or create the hash table entry for this database */
-       result = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-                                                                                               &databaseid,
-                                                                                               action, &found);
-
-       if (!create && !found)
-               return NULL;
-
-       /*
-        * If not found, initialize the new one.  This creates empty hash tables
-        * for tables and functions, too.
-        */
-       if (!found)
-               reset_dbentry_counters(result);
-
-       return result;
-}
 
-/*
- * Lookup the hash table entry for the specified table. If no hash
- * table entry exists, initialize it, if the create parameter is true.
- * Else, return NULL.
- */
-static PgStat_StatTabEntry *
-pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry, Oid tableoid, bool create)
-{
-       PgStat_StatTabEntry *result;
-       bool            found;
-       HASHACTION      action = (create ? HASH_ENTER : HASH_FIND);
-
-       /* Lookup or create the hash table entry for this table */
-       result = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                                                                &tableoid,
-                                                                                                action, &found);
-
-       if (!create && !found)
-               return NULL;
-
-       /* If not found, initialize the new one. */
-       if (!found)
-       {
-               result->numscans = 0;
-               result->tuples_returned = 0;
-               result->tuples_fetched = 0;
-               result->tuples_inserted = 0;
-               result->tuples_updated = 0;
-               result->tuples_deleted = 0;
-               result->tuples_hot_updated = 0;
-               result->n_live_tuples = 0;
-               result->n_dead_tuples = 0;
-               result->changes_since_analyze = 0;
-               result->inserts_since_vacuum = 0;
-               result->blocks_fetched = 0;
-               result->blocks_hit = 0;
-               result->vacuum_timestamp = 0;
-               result->vacuum_count = 0;
-               result->autovac_vacuum_timestamp = 0;
-               result->autovac_vacuum_count = 0;
-               result->analyze_timestamp = 0;
-               result->analyze_count = 0;
-               result->autovac_analyze_timestamp = 0;
-               result->autovac_analyze_count = 0;
-       }
-
-       return result;
-}
-
-/*
- * Return the entry of replication slot stats with the given name. Return
- * NULL if not found and the caller didn't request to create it.
- *
- * create tells whether to create the new slot entry if it is not found.
+/* ------------------------------------------------------------
+ * reading and writing of on-disk stats file
+ * ------------------------------------------------------------
  */
-static PgStat_StatReplSlotEntry *
-pgstat_get_replslot_entry(NameData name, bool create)
-{
-       PgStat_StatReplSlotEntry *slotent;
-       bool            found;
-
-       if (replSlotStatHash == NULL)
-       {
-               HASHCTL         hash_ctl;
-
-               /*
-                * Quick return NULL if the hash table is empty and the caller didn't
-                * request to create the entry.
-                */
-               if (!create)
-                       return NULL;
-
-               hash_ctl.keysize = sizeof(NameData);
-               hash_ctl.entrysize = sizeof(PgStat_StatReplSlotEntry);
-               replSlotStatHash = hash_create("Replication slots hash",
-                                                                          PGSTAT_REPLSLOT_HASH_SIZE,
-                                                                          &hash_ctl,
-                                                                          HASH_ELEM | HASH_BLOBS);
-       }
-
-       slotent = (PgStat_StatReplSlotEntry *) hash_search(replSlotStatHash,
-                                                                                                          (void *) &name,
-                                                                                                          create ? HASH_ENTER : HASH_FIND,
-                                                                                                          &found);
-
-       if (!slotent)
-       {
-               /* not found */
-               Assert(!create && !found);
-               return NULL;
-       }
-
-       /* initialize the entry */
-       if (create && !found)
-       {
-               namestrcpy(&(slotent->slotname), NameStr(name));
-               pgstat_reset_replslot_entry(slotent, 0);
-       }
 
-       return slotent;
-}
-
-/*
- * Reset the given replication slot stats.
- */
+/* helpers for pgstat_write_statsfile() */
 static void
-pgstat_reset_replslot_entry(PgStat_StatReplSlotEntry *slotent, TimestampTz ts)
+write_chunk(FILE *fpout, void *ptr, size_t len)
 {
-       /* reset only counters. Don't clear slot name */
-       slotent->spill_txns = 0;
-       slotent->spill_count = 0;
-       slotent->spill_bytes = 0;
-       slotent->stream_txns = 0;
-       slotent->stream_count = 0;
-       slotent->stream_bytes = 0;
-       slotent->total_txns = 0;
-       slotent->total_bytes = 0;
-       slotent->stat_reset_timestamp = ts;
-}
-
-/*
- * Return the subscription statistics entry with the given subscription OID.
- * If no subscription entry exists, initialize it, if the create parameter is
- * true.  Else, return NULL.
- */
-static PgStat_StatSubEntry *
-pgstat_get_subscription_entry(Oid subid, bool create)
-{
-       PgStat_StatSubEntry *subentry;
-       bool            found;
-       HASHACTION      action = (create ? HASH_ENTER : HASH_FIND);
-
-       if (subscriptionStatHash == NULL)
-       {
-               HASHCTL         hash_ctl;
-
-               /*
-                * Quick return NULL if the hash table is empty and the caller didn't
-                * request to create the entry.
-                */
-               if (!create)
-                       return NULL;
-
-               hash_ctl.keysize = sizeof(Oid);
-               hash_ctl.entrysize = sizeof(PgStat_StatSubEntry);
-               subscriptionStatHash = hash_create("Subscription hash",
-                                                                                  PGSTAT_SUBSCRIPTION_HASH_SIZE,
-                                                                                  &hash_ctl,
-                                                                                  HASH_ELEM | HASH_BLOBS);
-       }
-
-       subentry = (PgStat_StatSubEntry *) hash_search(subscriptionStatHash,
-                                                                                                  (void *) &subid,
-                                                                                                  action, &found);
-
-       if (!create && !found)
-               return NULL;
-
-       /* If not found, initialize the new one */
-       if (!found)
-               pgstat_reset_subscription(subentry, 0);
+       int                     rc;
 
-       return subentry;
-}
+       rc = fwrite(ptr, len, 1, fpout);
 
-/*
- * Reset the given subscription stats.
- */
-static void
-pgstat_reset_subscription(PgStat_StatSubEntry *subentry, TimestampTz ts)
-{
-       subentry->apply_error_count = 0;
-       subentry->sync_error_count = 0;
-       subentry->stat_reset_timestamp = ts;
+       /* we'll check for errors with ferror once at the end */
+       (void) rc;
 }
 
-
-/* ------------------------------------------------------------
- * reading and writing of on-disk stats file
- * ------------------------------------------------------------
- */
+#define write_chunk_s(fpout, ptr) write_chunk(fpout, ptr, sizeof(*ptr))
 
 /*
- * Write the global statistics file, as well as requested DB files.
- *
- * 'permanent' specifies writing to the permanent files not temporary ones.
- * When true (happens only when the collector is shutting down), also remove
- * the temporary files so that backends starting up under a new postmaster
- * can't read old data before the new collector is ready.
- *
- * When 'allDbs' is false, only the requested databases (listed in
- * pending_write_requests) will be written; otherwise, all databases
- * will be written.
+ * This function is called in the last process that is accessing the shared
+ * stats so locking is not required.
  */
 static void
-pgstat_write_statsfiles(bool permanent, bool allDbs)
+pgstat_write_statsfile(void)
 {
-       HASH_SEQ_STATUS hstat;
-       PgStat_StatDBEntry *dbentry;
        FILE       *fpout;
        int32           format_id;
-       const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
-       const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-       int                     rc;
+       const char *tmpfile = PGSTAT_STAT_PERMANENT_TMPFILE;
+       const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
+       dshash_seq_status hstat;
+       PgStatShared_HashEntry *ps;
+
+       pgstat_assert_is_up();
+
+       /* we're shutting down, so it's ok to just override this */
+       pgstat_fetch_consistency = PGSTAT_FETCH_CONSISTENCY_NONE;
 
        elog(DEBUG2, "writing stats file \"%s\"", statfile);
 
@@ -2141,105 +1252,100 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
                return;
        }
 
-       /*
-        * Set the timestamp of the stats file.
-        */
-       globalStats.stats_timestamp = GetCurrentTimestamp();
-
        /*
         * Write the file header --- currently just a format ID.
         */
        format_id = PGSTAT_FILE_FORMAT_ID;
-       rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
+       write_chunk_s(fpout, &format_id);
 
        /*
-        * Write global stats struct
+        * XXX: The following could now be generalized to just iterate over
+        * pgstat_kind_infos instead of knowing about the different kinds of
+        * stats.
         */
-       rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
 
        /*
         * Write archiver stats struct
         */
-       rc = fwrite(&archiverStats, sizeof(archiverStats), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
+       pgstat_build_snapshot_fixed(PGSTAT_KIND_ARCHIVER);
+       write_chunk_s(fpout, &pgStatLocal.snapshot.archiver);
 
        /*
-        * Write WAL stats struct
+        * Write bgwriter stats struct
         */
-       rc = fwrite(&walStats, sizeof(walStats), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
+       pgstat_build_snapshot_fixed(PGSTAT_KIND_BGWRITER);
+       write_chunk_s(fpout, &pgStatLocal.snapshot.bgwriter);
 
        /*
-        * Write SLRU stats struct
+        * Write checkpointer stats struct
         */
-       rc = fwrite(slruStats, sizeof(slruStats), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
+       pgstat_build_snapshot_fixed(PGSTAT_KIND_CHECKPOINTER);
+       write_chunk_s(fpout, &pgStatLocal.snapshot.checkpointer);
 
        /*
-        * Walk through the database table.
+        * Write SLRU stats struct
         */
-       hash_seq_init(&hstat, pgStatDBHash);
-       while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
-       {
-               /*
-                * Write out the table and function stats for this DB into the
-                * appropriate per-DB stat file, if required.
-                */
-               if (allDbs || pgstat_db_requested(dbentry->databaseid))
-               {
-                       /* Make DB's timestamp consistent with the global stats */
-                       dbentry->stats_timestamp = globalStats.stats_timestamp;
-
-                       pgstat_write_db_statsfile(dbentry, permanent);
-               }
-
-               /*
-                * Write out the DB entry. We don't write the tables or functions
-                * pointers, since they're of no use to any other process.
-                */
-               fputc('D', fpout);
-               rc = fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
-               (void) rc;                              /* we'll check for error with ferror */
-       }
+       pgstat_build_snapshot_fixed(PGSTAT_KIND_SLRU);
+       write_chunk_s(fpout, &pgStatLocal.snapshot.slru);
 
        /*
-        * Write replication slot stats struct
+        * Write WAL stats struct
         */
-       if (replSlotStatHash)
-       {
-               PgStat_StatReplSlotEntry *slotent;
-
-               hash_seq_init(&hstat, replSlotStatHash);
-               while ((slotent = (PgStat_StatReplSlotEntry *) hash_seq_search(&hstat)) != NULL)
-               {
-                       fputc('R', fpout);
-                       rc = fwrite(slotent, sizeof(PgStat_StatReplSlotEntry), 1, fpout);
-                       (void) rc;                      /* we'll check for error with ferror */
-               }
-       }
+       pgstat_build_snapshot_fixed(PGSTAT_KIND_WAL);
+       write_chunk_s(fpout, &pgStatLocal.snapshot.wal);
 
        /*
-        * Write subscription stats struct
+        * Walk through the stats entries
         */
-       if (subscriptionStatHash)
+       dshash_seq_init(&hstat, pgStatLocal.shared_hash, false);
+       while ((ps = dshash_seq_next(&hstat)) != NULL)
        {
-               PgStat_StatSubEntry *subentry;
+               PgStatShared_Common *shstats;
+               const PgStat_KindInfo *kind_info = NULL;
+
+               CHECK_FOR_INTERRUPTS();
+
+               /* we may have some "dropped" entries not yet removed, skip them */
+               Assert(!ps->dropped);
+               if (ps->dropped)
+                       continue;
+
+               shstats = (PgStatShared_Common *) dsa_get_address(pgStatLocal.dsa, ps->body);
+
+               kind_info = pgstat_get_kind_info(ps->key.kind);
+
+               /* if not dropped the valid-entry refcount should exist */
+               Assert(pg_atomic_read_u32(&ps->refcount) > 0);
 
-               hash_seq_init(&hstat, subscriptionStatHash);
-               while ((subentry = (PgStat_StatSubEntry *) hash_seq_search(&hstat)) != NULL)
+               if (!kind_info->to_serialized_name)
                {
+                       /* normal stats entry, identified by PgStat_HashKey */
                        fputc('S', fpout);
-                       rc = fwrite(subentry, sizeof(PgStat_StatSubEntry), 1, fpout);
-                       (void) rc;                      /* we'll check for error with ferror */
+                       write_chunk_s(fpout, &ps->key);
                }
+               else
+               {
+                       /* stats entry identified by name on disk (e.g. slots) */
+                       NameData        name;
+
+                       kind_info->to_serialized_name(shstats, &name);
+
+                       fputc('N', fpout);
+                       write_chunk_s(fpout, &ps->key.kind);
+                       write_chunk_s(fpout, &name);
+               }
+
+               /* Write except the header part of the entry */
+               write_chunk(fpout,
+                                       pgstat_get_entry_data(ps->key.kind, shstats),
+                                       pgstat_get_entry_len(ps->key.kind));
        }
+       dshash_seq_term(&hstat);
 
        /*
         * No more output to be done. Close the temp file and replace the old
         * pgstat.stat with it.  The ferror() check replaces testing for error
-        * after each individual fputc or fwrite above.
+        * after each individual fputc or fwrite (in write_chunk()) above.
         */
        fputc('E', fpout);
 
@@ -2268,1939 +1374,230 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
                                                tmpfile, statfile)));
                unlink(tmpfile);
        }
+}
 
-       if (permanent)
-               unlink(pgstat_stat_filename);
-
-       /*
-        * Now throw away the list of requests.  Note that requests sent after we
-        * started the write are still waiting on the network socket.
-        */
-       list_free(pending_write_requests);
-       pending_write_requests = NIL;
-}
-
-/*
- * return the filename for a DB stat file; filename is the output buffer,
- * of length len.
- */
-static void
-get_dbstat_filename(bool permanent, bool tempname, Oid databaseid,
-                                       char *filename, int len)
+/* helpers for pgstat_read_statsfile() */
+static bool
+read_chunk(FILE *fpin, void *ptr, size_t len)
 {
-       int                     printed;
-
-       /* NB -- pgstat_reset_remove_files knows about the pattern this uses */
-       printed = snprintf(filename, len, "%s/db_%u.%s",
-                                          permanent ? PGSTAT_STAT_PERMANENT_DIRECTORY :
-                                          pgstat_stat_directory,
-                                          databaseid,
-                                          tempname ? "tmp" : "stat");
-       if (printed >= len)
-               elog(ERROR, "overlength pgstat path");
+       return fread(ptr, 1, len, fpin) == len;
 }
 
-/*
- * Write the stat file for a single database.
- *
- * If writing to the permanent file (happens when the collector is
- * shutting down only), remove the temporary file so that backends
- * starting up under a new postmaster can't read the old data before
- * the new collector is ready.
- */
-static void
-pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
-{
-       HASH_SEQ_STATUS tstat;
-       HASH_SEQ_STATUS fstat;
-       PgStat_StatTabEntry *tabentry;
-       PgStat_StatFuncEntry *funcentry;
-       FILE       *fpout;
-       int32           format_id;
-       Oid                     dbid = dbentry->databaseid;
-       int                     rc;
-       char            tmpfile[MAXPGPATH];
-       char            statfile[MAXPGPATH];
-
-       get_dbstat_filename(permanent, true, dbid, tmpfile, MAXPGPATH);
-       get_dbstat_filename(permanent, false, dbid, statfile, MAXPGPATH);
-
-       elog(DEBUG2, "writing stats file \"%s\"", statfile);
-
-       /*
-        * Open the statistics temp file to write out the current values.
-        */
-       fpout = AllocateFile(tmpfile, PG_BINARY_W);
-       if (fpout == NULL)
-       {
-               ereport(LOG,
-                               (errcode_for_file_access(),
-                                errmsg("could not open temporary statistics file \"%s\": %m",
-                                               tmpfile)));
-               return;
-       }
-
-       /*
-        * Write the file header --- currently just a format ID.
-        */
-       format_id = PGSTAT_FILE_FORMAT_ID;
-       rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
-       (void) rc;                                      /* we'll check for error with ferror */
-
-       /*
-        * Walk through the database's access stats per table.
-        */
-       hash_seq_init(&tstat, dbentry->tables);
-       while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
-       {
-               fputc('T', fpout);
-               rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
-               (void) rc;                              /* we'll check for error with ferror */
-       }
-
-       /*
-        * Walk through the database's function stats table.
-        */
-       hash_seq_init(&fstat, dbentry->functions);
-       while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
-       {
-               fputc('F', fpout);
-               rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
-               (void) rc;                              /* we'll check for error with ferror */
-       }
-
-       /*
-        * No more output to be done. Close the temp file and replace the old
-        * pgstat.stat with it.  The ferror() check replaces testing for error
-        * after each individual fputc or fwrite above.
-        */
-       fputc('E', fpout);
-
-       if (ferror(fpout))
-       {
-               ereport(LOG,
-                               (errcode_for_file_access(),
-                                errmsg("could not write temporary statistics file \"%s\": %m",
-                                               tmpfile)));
-               FreeFile(fpout);
-               unlink(tmpfile);
-       }
-       else if (FreeFile(fpout) < 0)
-       {
-               ereport(LOG,
-                               (errcode_for_file_access(),
-                                errmsg("could not close temporary statistics file \"%s\": %m",
-                                               tmpfile)));
-               unlink(tmpfile);
-       }
-       else if (rename(tmpfile, statfile) < 0)
-       {
-               ereport(LOG,
-                               (errcode_for_file_access(),
-                                errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
-                                               tmpfile, statfile)));
-               unlink(tmpfile);
-       }
-
-       if (permanent)
-       {
-               get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
-
-               elog(DEBUG2, "removing temporary stats file \"%s\"", statfile);
-               unlink(statfile);
-       }
-}
+#define read_chunk_s(fpin, ptr) read_chunk(fpin, ptr, sizeof(*ptr))
 
 /*
- * Reads in some existing statistics collector files and returns the
- * databases hash table that is the top level of the data.
+ * Reads in existing statistics file into the shared stats hash.
  *
- * If 'onlydb' is not InvalidOid, it means we only want data for that DB
- * plus the shared catalogs ("DB 0").  We'll still populate the DB hash
- * table for all databases, but we don't bother even creating table/function
- * hash tables for other databases.
- *
- * 'permanent' specifies reading from the permanent files not temporary ones.
- * When true (happens only when the collector is starting up), remove the
- * files after reading; the in-memory status is now authoritative, and the
- * files would be out of date in case somebody else reads them.
- *
- * If a 'deep' read is requested, table/function stats are read, otherwise
- * the table/function hash tables remain empty.
+ * This function is called in the only process that is accessing the shared
+ * stats so locking is not required.
  */
-static HTAB *
-pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
+static void
+pgstat_read_statsfile(void)
 {
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatDBEntry dbbuf;
-       HASHCTL         hash_ctl;
-       HTAB       *dbhash;
        FILE       *fpin;
        int32           format_id;
        bool            found;
-       const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-       int                     i;
-       TimestampTz ts;
-
-       /*
-        * The tables will live in pgStatLocalContext.
-        */
-       pgstat_setup_memcxt();
-
-       /*
-        * Create the DB hashtable
-        */
-       hash_ctl.keysize = sizeof(Oid);
-       hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
-       hash_ctl.hcxt = pgStatLocalContext;
-       dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
-                                                HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-       /*
-        * Clear out global, archiver, WAL and SLRU statistics so they start from
-        * zero in case we can't load an existing statsfile.
-        */
-       memset(&globalStats, 0, sizeof(globalStats));
-       memset(&archiverStats, 0, sizeof(archiverStats));
-       memset(&walStats, 0, sizeof(walStats));
-       memset(&slruStats, 0, sizeof(slruStats));
+       const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
+       PgStat_ShmemControl *shmem = pgStatLocal.shmem;
+       TimestampTz ts = GetCurrentTimestamp();
 
-       /*
-        * Set the current timestamp (will be kept only in case we can't load an
-        * existing statsfile).
-        */
-       ts = GetCurrentTimestamp();
-       globalStats.bgwriter.stat_reset_timestamp = ts;
-       archiverStats.stat_reset_timestamp = ts;
-       walStats.stat_reset_timestamp = ts;
+       /* shouldn't be called from postmaster */
+       Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
 
-       /*
-        * Set the same reset timestamp for all SLRU items too.
-        */
-       for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
-               slruStats[i].stat_reset_timestamp = ts;
+       elog(DEBUG2, "reading stats file \"%s\"", statfile);
 
        /*
         * Try to open the stats file. If it doesn't exist, the backends simply
-        * return zero for anything and the collector simply starts from scratch
+        * returns zero for anything and statistics simply starts from scratch
         * with empty counters.
         *
-        * ENOENT is a possibility if the stats collector is not running or has
-        * not yet written the stats file the first time.  Any other failure
-        * condition is suspicious.
+        * ENOENT is a possibility if stats collection was previously disabled or
+        * has not yet written the stats file for the first time.  Any other
+        * failure condition is suspicious.
         */
        if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
        {
                if (errno != ENOENT)
-                       ereport(pgStatRunningInCollector ? LOG : WARNING,
+                       ereport(LOG,
                                        (errcode_for_file_access(),
                                         errmsg("could not open statistics file \"%s\": %m",
                                                        statfile)));
-               return dbhash;
+               pgstat_reset_after_failure(ts);
+               return;
        }
 
        /*
         * Verify it's of the expected format.
         */
-       if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
+       if (!read_chunk_s(fpin, &format_id) ||
                format_id != PGSTAT_FILE_FORMAT_ID)
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               goto done;
-       }
+               goto error;
 
        /*
-        * Read global stats struct
+        * XXX: The following could now be generalized to just iterate over
+        * pgstat_kind_infos instead of knowing about the different kinds of
+        * stats.
         */
-       if (fread(&globalStats, 1, sizeof(globalStats), fpin) != sizeof(globalStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               memset(&globalStats, 0, sizeof(globalStats));
-               goto done;
-       }
 
        /*
-        * In the collector, disregard the timestamp we read from the permanent
-        * stats file; we should be willing to write a temp stats file immediately
-        * upon the first request from any backend.  This only matters if the old
-        * file's timestamp is less than PGSTAT_STAT_INTERVAL ago, but that's not
-        * an unusual scenario.
+        * Read archiver stats struct
         */
-       if (pgStatRunningInCollector)
-               globalStats.stats_timestamp = 0;
+       if (!read_chunk_s(fpin, &shmem->archiver.stats))
+               goto error;
 
        /*
-        * Read archiver stats struct
+        * Read bgwriter stats struct
         */
-       if (fread(&archiverStats, 1, sizeof(archiverStats), fpin) != sizeof(archiverStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               memset(&archiverStats, 0, sizeof(archiverStats));
-               goto done;
-       }
+       if (!read_chunk_s(fpin, &shmem->bgwriter.stats))
+               goto error;
 
        /*
-        * Read WAL stats struct
+        * Read checkpointer stats struct
         */
-       if (fread(&walStats, 1, sizeof(walStats), fpin) != sizeof(walStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               memset(&walStats, 0, sizeof(walStats));
-               goto done;
-       }
+       if (!read_chunk_s(fpin, &shmem->checkpointer.stats))
+               goto error;
 
        /*
         * Read SLRU stats struct
         */
-       if (fread(slruStats, 1, sizeof(slruStats), fpin) != sizeof(slruStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               memset(&slruStats, 0, sizeof(slruStats));
-               goto done;
-       }
+       if (!read_chunk_s(fpin, &shmem->slru.stats))
+               goto error;
+
+       /*
+        * Read WAL stats struct
+        */
+       if (!read_chunk_s(fpin, &shmem->wal.stats))
+               goto error;
 
        /*
-        * We found an existing collector stats file. Read it and put all the
-        * hashtable entries into place.
+        * We found an existing statistics file. Read it and put all the hash
+        * table entries into place.
         */
        for (;;)
        {
-               switch (fgetc(fpin))
-               {
-                               /*
-                                * 'D'  A PgStat_StatDBEntry struct describing a database
-                                * follows.
-                                */
-                       case 'D':
-                               if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, tables),
-                                                 fpin) != offsetof(PgStat_StatDBEntry, tables))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
-
-                               /*
-                                * Add to the DB hash
-                                */
-                               dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
-                                                                                                                        (void *) &dbbuf.databaseid,
-                                                                                                                        HASH_ENTER,
-                                                                                                                        &found);
-                               if (found)
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
+               char            t = fgetc(fpin);
 
-                               memcpy(dbentry, &dbbuf, sizeof(PgStat_StatDBEntry));
-                               dbentry->tables = NULL;
-                               dbentry->functions = NULL;
-
-                               /*
-                                * In the collector, disregard the timestamp we read from the
-                                * permanent stats file; we should be willing to write a temp
-                                * stats file immediately upon the first request from any
-                                * backend.
-                                */
-                               if (pgStatRunningInCollector)
-                                       dbentry->stats_timestamp = 0;
-
-                               /*
-                                * Don't create tables/functions hashtables for uninteresting
-                                * databases.
-                                */
-                               if (onlydb != InvalidOid)
+               switch (t)
+               {
+                       case 'S':
+                       case 'N':
                                {
-                                       if (dbbuf.databaseid != onlydb &&
-                                               dbbuf.databaseid != InvalidOid)
-                                               break;
-                               }
+                                       PgStat_HashKey key;
+                                       PgStatShared_HashEntry *p;
+                                       PgStatShared_Common *header;
 
-                               hash_ctl.keysize = sizeof(Oid);
-                               hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-                               hash_ctl.hcxt = pgStatLocalContext;
-                               dbentry->tables = hash_create("Per-database table",
-                                                                                         PGSTAT_TAB_HASH_SIZE,
-                                                                                         &hash_ctl,
-                                                                                         HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-                               hash_ctl.keysize = sizeof(Oid);
-                               hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-                               hash_ctl.hcxt = pgStatLocalContext;
-                               dbentry->functions = hash_create("Per-database function",
-                                                                                                PGSTAT_FUNCTION_HASH_SIZE,
-                                                                                                &hash_ctl,
-                                                                                                HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-                               /*
-                                * If requested, read the data from the database-specific
-                                * file.  Otherwise we just leave the hashtables empty.
-                                */
-                               if (deep)
-                                       pgstat_read_db_statsfile(dbentry->databaseid,
-                                                                                        dbentry->tables,
-                                                                                        dbentry->functions,
-                                                                                        permanent);
-
-                               break;
-
-                               /*
-                                * 'R'  A PgStat_StatReplSlotEntry struct describing a
-                                * replication slot follows.
-                                */
-                       case 'R':
-                               {
-                                       PgStat_StatReplSlotEntry slotbuf;
-                                       PgStat_StatReplSlotEntry *slotent;
+                                       CHECK_FOR_INTERRUPTS();
 
-                                       if (fread(&slotbuf, 1, sizeof(PgStat_StatReplSlotEntry), fpin)
-                                               != sizeof(PgStat_StatReplSlotEntry))
+                                       if (t == 'S')
                                        {
-                                               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                               (errmsg("corrupted statistics file \"%s\"",
-                                                                               statfile)));
-                                               goto done;
-                                       }
+                                               /* normal stats entry, identified by PgStat_HashKey */
+                                               if (!read_chunk_s(fpin, &key))
+                                                       goto error;
 
-                                       /* Create hash table if we don't have it already. */
-                                       if (replSlotStatHash == NULL)
-                                       {
-                                               HASHCTL         hash_ctl;
-
-                                               hash_ctl.keysize = sizeof(NameData);
-                                               hash_ctl.entrysize = sizeof(PgStat_StatReplSlotEntry);
-                                               hash_ctl.hcxt = pgStatLocalContext;
-                                               replSlotStatHash = hash_create("Replication slots hash",
-                                                                                                          PGSTAT_REPLSLOT_HASH_SIZE,
-                                                                                                          &hash_ctl,
-                                                                                                          HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+                                               if (!pgstat_is_kind_valid(key.kind))
+                                                       goto error;
                                        }
+                                       else
+                                       {
+                                               /* stats entry identified by name on disk (e.g. slots) */
+                                               const PgStat_KindInfo *kind_info = NULL;
+                                               PgStat_Kind kind;
+                                               NameData        name;
 
-                                       slotent = (PgStat_StatReplSlotEntry *) hash_search(replSlotStatHash,
-                                                                                                                                          (void *) &slotbuf.slotname,
-                                                                                                                                          HASH_ENTER, NULL);
-                                       memcpy(slotent, &slotbuf, sizeof(PgStat_StatReplSlotEntry));
-                                       break;
-                               }
+                                               if (!read_chunk_s(fpin, &kind))
+                                                       goto error;
+                                               if (!read_chunk_s(fpin, &name))
+                                                       goto error;
+                                               if (!pgstat_is_kind_valid(kind))
+                                                       goto error;
 
-                               /*
-                                * 'S'  A PgStat_StatSubEntry struct describing subscription
-                                * statistics.
-                                */
-                       case 'S':
-                               {
-                                       PgStat_StatSubEntry subbuf;
-                                       PgStat_StatSubEntry *subentry;
+                                               kind_info = pgstat_get_kind_info(kind);
 
-                                       if (fread(&subbuf, 1, sizeof(PgStat_StatSubEntry), fpin)
-                                               != sizeof(PgStat_StatSubEntry))
-                                       {
-                                               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                               (errmsg("corrupted statistics file \"%s\"",
-                                                                               statfile)));
-                                               goto done;
+                                               if (!kind_info->from_serialized_name)
+                                                       goto error;
+
+                                               if (!kind_info->from_serialized_name(&name, &key))
+                                               {
+                                                       /* skip over data for entry we don't care about */
+                                                       if (fseek(fpin, pgstat_get_entry_len(kind), SEEK_CUR) != 0)
+                                                               goto error;
+
+                                                       continue;
+                                               }
+
+                                               Assert(key.kind == kind);
                                        }
 
-                                       if (subscriptionStatHash == NULL)
+                                       /*
+                                        * This intentionally doesn't use pgstat_get_entry_ref() -
+                                        * putting all stats into checkpointer's
+                                        * pgStatEntryRefHash would be wasted effort and memory.
+                                        */
+                                       p = dshash_find_or_insert(pgStatLocal.shared_hash, &key, &found);
+
+                                       /* don't allow duplicate entries */
+                                       if (found)
                                        {
-                                               HASHCTL         hash_ctl;
-
-                                               hash_ctl.keysize = sizeof(Oid);
-                                               hash_ctl.entrysize = sizeof(PgStat_StatSubEntry);
-                                               hash_ctl.hcxt = pgStatLocalContext;
-                                               subscriptionStatHash = hash_create("Subscription hash",
-                                                                                                                  PGSTAT_SUBSCRIPTION_HASH_SIZE,
-                                                                                                                  &hash_ctl,
-                                                                                                                  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+                                               dshash_release_lock(pgStatLocal.shared_hash, p);
+                                               elog(WARNING, "found duplicate stats entry %d/%u/%u",
+                                                        key.kind, key.dboid, key.objoid);
+                                               goto error;
                                        }
 
-                                       subentry = (PgStat_StatSubEntry *) hash_search(subscriptionStatHash,
-                                                                                                                                  (void *) &subbuf.subid,
-                                                                                                                                  HASH_ENTER, NULL);
+                                       header = pgstat_init_entry(key.kind, p);
+                                       dshash_release_lock(pgStatLocal.shared_hash, p);
+
+                                       if (!read_chunk(fpin,
+                                                                       pgstat_get_entry_data(key.kind, header),
+                                                                       pgstat_get_entry_len(key.kind)))
+                                               goto error;
 
-                                       memcpy(subentry, &subbuf, sizeof(subbuf));
                                        break;
                                }
-
                        case 'E':
                                goto done;
 
                        default:
-                               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                               (errmsg("corrupted statistics file \"%s\"",
-                                                               statfile)));
-                               goto done;
+                               goto error;
                }
        }
 
 done:
        FreeFile(fpin);
 
-       /* If requested to read the permanent file, also get rid of it. */
-       if (permanent)
-       {
-               elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-               unlink(statfile);
-       }
-
-       return dbhash;
-}
-
-
-/*
- * Reads in the existing statistics collector file for the given database,
- * filling the passed-in tables and functions hash tables.
- *
- * As in pgstat_read_statsfiles, if the permanent file is requested, it is
- * removed after reading.
- *
- * Note: this code has the ability to skip storing per-table or per-function
- * data, if NULL is passed for the corresponding hashtable.  That's not used
- * at the moment though.
- */
-static void
-pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
-                                                bool permanent)
-{
-       PgStat_StatTabEntry *tabentry;
-       PgStat_StatTabEntry tabbuf;
-       PgStat_StatFuncEntry funcbuf;
-       PgStat_StatFuncEntry *funcentry;
-       FILE       *fpin;
-       int32           format_id;
-       bool            found;
-       char            statfile[MAXPGPATH];
-
-       get_dbstat_filename(permanent, false, databaseid, statfile, MAXPGPATH);
-
-       /*
-        * Try to open the stats file. If it doesn't exist, the backends simply
-        * return zero for anything and the collector simply starts from scratch
-        * with empty counters.
-        *
-        * ENOENT is a possibility if the stats collector is not running or has
-        * not yet written the stats file the first time.  Any other failure
-        * condition is suspicious.
-        */
-       if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-       {
-               if (errno != ENOENT)
-                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                       (errcode_for_file_access(),
-                                        errmsg("could not open statistics file \"%s\": %m",
-                                                       statfile)));
-               return;
-       }
-
-       /*
-        * Verify it's of the expected format.
-        */
-       if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-               format_id != PGSTAT_FILE_FORMAT_ID)
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               goto done;
-       }
-
-       /*
-        * We found an existing collector stats file. Read it and put all the
-        * hashtable entries into place.
-        */
-       for (;;)
-       {
-               switch (fgetc(fpin))
-               {
-                               /*
-                                * 'T'  A PgStat_StatTabEntry follows.
-                                */
-                       case 'T':
-                               if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
-                                                 fpin) != sizeof(PgStat_StatTabEntry))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
-
-                               /*
-                                * Skip if table data not wanted.
-                                */
-                               if (tabhash == NULL)
-                                       break;
-
-                               tabentry = (PgStat_StatTabEntry *) hash_search(tabhash,
-                                                                                                                          (void *) &tabbuf.tableid,
-                                                                                                                          HASH_ENTER, &found);
-
-                               if (found)
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
-
-                               memcpy(tabentry, &tabbuf, sizeof(tabbuf));
-                               break;
-
-                               /*
-                                * 'F'  A PgStat_StatFuncEntry follows.
-                                */
-                       case 'F':
-                               if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
-                                                 fpin) != sizeof(PgStat_StatFuncEntry))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
-
-                               /*
-                                * Skip if function data not wanted.
-                                */
-                               if (funchash == NULL)
-                                       break;
-
-                               funcentry = (PgStat_StatFuncEntry *) hash_search(funchash,
-                                                                                                                                (void *) &funcbuf.functionid,
-                                                                                                                                HASH_ENTER, &found);
-
-                               if (found)
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       goto done;
-                               }
+       elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
+       unlink(statfile);
 
-                               memcpy(funcentry, &funcbuf, sizeof(funcbuf));
-                               break;
-
-                               /*
-                                * 'E'  The EOF marker of a complete stats file.
-                                */
-                       case 'E':
-                               goto done;
+       return;
 
-                       default:
-                               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                               (errmsg("corrupted statistics file \"%s\"",
-                                                               statfile)));
-                               goto done;
-               }
-       }
+error:
+       ereport(LOG,
+                       (errmsg("corrupted statistics file \"%s\"", statfile)));
 
-done:
-       FreeFile(fpin);
+       /* Set the current timestamp as reset timestamp */
+       pgstat_reset_after_failure(ts);
 
-       if (permanent)
-       {
-               elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-               unlink(statfile);
-       }
+       goto done;
 }
 
 /*
- * Attempt to determine the timestamp of the last db statfile write.
- * Returns true if successful; the timestamp is stored in *ts. The caller must
- * rely on timestamp stored in *ts iff the function returns true.
- *
- * This needs to be careful about handling databases for which no stats file
- * exists, such as databases without a stat entry or those not yet written:
- *
- * - if there's a database entry in the global file, return the corresponding
- * stats_timestamp value.
- *
- * - if there's no db stat entry (e.g. for a new or inactive database),
- * there's no stats_timestamp value, but also nothing to write so we return
- * the timestamp of the global statfile.
+ * Helper to reset / drop stats after restoring stats from disk failed,
+ * potentially after already loading parts.
  */
-static bool
-pgstat_read_db_statsfile_timestamp(Oid databaseid, bool permanent,
-                                                                  TimestampTz *ts)
+static void
+pgstat_reset_after_failure(TimestampTz ts)
 {
-       PgStat_StatDBEntry dbentry;
-       PgStat_GlobalStats myGlobalStats;
-       PgStat_ArchiverStats myArchiverStats;
-       PgStat_WalStats myWalStats;
-       PgStat_SLRUStats mySLRUStats[SLRU_NUM_ELEMENTS];
-       PgStat_StatReplSlotEntry myReplSlotStats;
-       PgStat_StatSubEntry mySubStats;
-       FILE       *fpin;
-       int32           format_id;
-       const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-
-       /*
-        * Try to open the stats file.  As above, anything but ENOENT is worthy of
-        * complaining about.
-        */
-       if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-       {
-               if (errno != ENOENT)
-                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                       (errcode_for_file_access(),
-                                        errmsg("could not open statistics file \"%s\": %m",
-                                                       statfile)));
-               return false;
-       }
-
-       /*
-        * Verify it's of the expected format.
-        */
-       if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-               format_id != PGSTAT_FILE_FORMAT_ID)
+       /* reset fixed-numbered stats */
+       for (int kind = PGSTAT_KIND_FIRST_VALID; kind <= PGSTAT_KIND_LAST; kind++)
        {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               FreeFile(fpin);
-               return false;
-       }
+               const PgStat_KindInfo *kind_info = pgstat_get_kind_info(kind);
 
-       /*
-        * Read global stats struct
-        */
-       if (fread(&myGlobalStats, 1, sizeof(myGlobalStats),
-                         fpin) != sizeof(myGlobalStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               FreeFile(fpin);
-               return false;
-       }
+               if (!kind_info->fixed_amount)
+                       continue;
 
-       /*
-        * Read archiver stats struct
-        */
-       if (fread(&myArchiverStats, 1, sizeof(myArchiverStats),
-                         fpin) != sizeof(myArchiverStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               FreeFile(fpin);
-               return false;
+               kind_info->reset_all_cb(ts);
        }
 
-       /*
-        * Read WAL stats struct
-        */
-       if (fread(&myWalStats, 1, sizeof(myWalStats), fpin) != sizeof(myWalStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               FreeFile(fpin);
-               return false;
-       }
-
-       /*
-        * Read SLRU stats struct
-        */
-       if (fread(mySLRUStats, 1, sizeof(mySLRUStats), fpin) != sizeof(mySLRUStats))
-       {
-               ereport(pgStatRunningInCollector ? LOG : WARNING,
-                               (errmsg("corrupted statistics file \"%s\"", statfile)));
-               FreeFile(fpin);
-               return false;
-       }
-
-       /* By default, we're going to return the timestamp of the global file. */
-       *ts = myGlobalStats.stats_timestamp;
-
-       /*
-        * We found an existing collector stats file.  Read it and look for a
-        * record for the requested database.  If found, use its timestamp.
-        */
-       for (;;)
-       {
-               switch (fgetc(fpin))
-               {
-                               /*
-                                * 'D'  A PgStat_StatDBEntry struct describing a database
-                                * follows.
-                                */
-                       case 'D':
-                               if (fread(&dbentry, 1, offsetof(PgStat_StatDBEntry, tables),
-                                                 fpin) != offsetof(PgStat_StatDBEntry, tables))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       FreeFile(fpin);
-                                       return false;
-                               }
-
-                               /*
-                                * If this is the DB we're looking for, save its timestamp and
-                                * we're done.
-                                */
-                               if (dbentry.databaseid == databaseid)
-                               {
-                                       *ts = dbentry.stats_timestamp;
-                                       goto done;
-                               }
-
-                               break;
-
-                               /*
-                                * 'R'  A PgStat_StatReplSlotEntry struct describing a
-                                * replication slot follows.
-                                */
-                       case 'R':
-                               if (fread(&myReplSlotStats, 1, sizeof(PgStat_StatReplSlotEntry), fpin)
-                                       != sizeof(PgStat_StatReplSlotEntry))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       FreeFile(fpin);
-                                       return false;
-                               }
-                               break;
-
-                               /*
-                                * 'S'  A PgStat_StatSubEntry struct describing subscription
-                                * statistics follows.
-                                */
-                       case 'S':
-                               if (fread(&mySubStats, 1, sizeof(PgStat_StatSubEntry), fpin)
-                                       != sizeof(PgStat_StatSubEntry))
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       FreeFile(fpin);
-                                       return false;
-                               }
-                               break;
-
-                       case 'E':
-                               goto done;
-
-                       default:
-                               {
-                                       ereport(pgStatRunningInCollector ? LOG : WARNING,
-                                                       (errmsg("corrupted statistics file \"%s\"",
-                                                                       statfile)));
-                                       FreeFile(fpin);
-                                       return false;
-                               }
-               }
-       }
-
-done:
-       FreeFile(fpin);
-       return true;
-}
-
-/*
- * If not already done, read the statistics collector stats file into
- * some hash tables.  The results will be kept until pgstat_clear_snapshot()
- * is called (typically, at end of transaction).
- */
-static void
-backend_read_statsfile(void)
-{
-       TimestampTz min_ts = 0;
-       TimestampTz ref_ts = 0;
-       Oid                     inquiry_db;
-       int                     count;
-
-       pgstat_assert_is_up();
-
-       /* already read it? */
-       if (pgStatDBHash)
-               return;
-       Assert(!pgStatRunningInCollector);
-
-       /*
-        * In a normal backend, we check staleness of the data for our own DB, and
-        * so we send MyDatabaseId in inquiry messages.  In the autovac launcher,
-        * check staleness of the shared-catalog data, and send InvalidOid in
-        * inquiry messages so as not to force writing unnecessary data.
-        */
-       if (IsAutoVacuumLauncherProcess())
-               inquiry_db = InvalidOid;
-       else
-               inquiry_db = MyDatabaseId;
-
-       /*
-        * Loop until fresh enough stats file is available or we ran out of time.
-        * The stats inquiry message is sent repeatedly in case collector drops
-        * it; but not every single time, as that just swamps the collector.
-        */
-       for (count = 0; count < PGSTAT_POLL_LOOP_COUNT; count++)
-       {
-               bool            ok;
-               TimestampTz file_ts = 0;
-               TimestampTz cur_ts;
-
-               CHECK_FOR_INTERRUPTS();
-
-               ok = pgstat_read_db_statsfile_timestamp(inquiry_db, false, &file_ts);
-
-               cur_ts = GetCurrentTimestamp();
-               /* Calculate min acceptable timestamp, if we didn't already */
-               if (count == 0 || cur_ts < ref_ts)
-               {
-                       /*
-                        * We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL
-                        * msec before now.  This indirectly ensures that the collector
-                        * needn't write the file more often than PGSTAT_STAT_INTERVAL. In
-                        * an autovacuum worker, however, we want a lower delay to avoid
-                        * using stale data, so we use PGSTAT_RETRY_DELAY (since the
-                        * number of workers is low, this shouldn't be a problem).
-                        *
-                        * We don't recompute min_ts after sleeping, except in the
-                        * unlikely case that cur_ts went backwards.  So we might end up
-                        * accepting a file a bit older than PGSTAT_STAT_INTERVAL.  In
-                        * practice that shouldn't happen, though, as long as the sleep
-                        * time is less than PGSTAT_STAT_INTERVAL; and we don't want to
-                        * tell the collector that our cutoff time is less than what we'd
-                        * actually accept.
-                        */
-                       ref_ts = cur_ts;
-                       if (IsAutoVacuumWorkerProcess())
-                               min_ts = TimestampTzPlusMilliseconds(ref_ts,
-                                                                                                        -PGSTAT_RETRY_DELAY);
-                       else
-                               min_ts = TimestampTzPlusMilliseconds(ref_ts,
-                                                                                                        -PGSTAT_STAT_INTERVAL);
-               }
-
-               /*
-                * If the file timestamp is actually newer than cur_ts, we must have
-                * had a clock glitch (system time went backwards) or there is clock
-                * skew between our processor and the stats collector's processor.
-                * Accept the file, but send an inquiry message anyway to make
-                * pgstat_recv_inquiry do a sanity check on the collector's time.
-                */
-               if (ok && file_ts > cur_ts)
-               {
-                       /*
-                        * A small amount of clock skew between processors isn't terribly
-                        * surprising, but a large difference is worth logging.  We
-                        * arbitrarily define "large" as 1000 msec.
-                        */
-                       if (file_ts >= TimestampTzPlusMilliseconds(cur_ts, 1000))
-                       {
-                               char       *filetime;
-                               char       *mytime;
-
-                               /* Copy because timestamptz_to_str returns a static buffer */
-                               filetime = pstrdup(timestamptz_to_str(file_ts));
-                               mytime = pstrdup(timestamptz_to_str(cur_ts));
-                               ereport(LOG,
-                                               (errmsg("statistics collector's time %s is later than backend local time %s",
-                                                               filetime, mytime)));
-                               pfree(filetime);
-                               pfree(mytime);
-                       }
-
-                       pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-                       break;
-               }
-
-               /* Normal acceptance case: file is not older than cutoff time */
-               if (ok && file_ts >= min_ts)
-                       break;
-
-               /* Not there or too old, so kick the collector and wait a bit */
-               if ((count % PGSTAT_INQ_LOOP_COUNT) == 0)
-                       pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-
-               pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
-       }
-
-       if (count >= PGSTAT_POLL_LOOP_COUNT)
-               ereport(LOG,
-                               (errmsg("using stale statistics instead of current ones "
-                                               "because stats collector is not responding")));
-
-       /*
-        * Autovacuum launcher wants stats about all databases, but a shallow read
-        * is sufficient.  Regular backends want a deep read for just the tables
-        * they can see (MyDatabaseId + shared catalogs).
-        */
-       if (IsAutoVacuumLauncherProcess())
-               pgStatDBHash = pgstat_read_statsfiles(InvalidOid, false, false);
-       else
-               pgStatDBHash = pgstat_read_statsfiles(MyDatabaseId, false, true);
-}
-
-/*
- * Do we need to write out any stats files?
- */
-static bool
-pgstat_write_statsfile_needed(void)
-{
-       if (pending_write_requests != NIL)
-               return true;
-
-       /* Everything was written recently */
-       return false;
-}
-
-/*
- * Checks whether stats for a particular DB need to be written to a file.
- */
-static bool
-pgstat_db_requested(Oid databaseid)
-{
-       /*
-        * If any requests are outstanding at all, we should write the stats for
-        * shared catalogs (the "database" with OID 0).  This ensures that
-        * backends will see up-to-date stats for shared catalogs, even though
-        * they send inquiry messages mentioning only their own DB.
-        */
-       if (databaseid == InvalidOid && pending_write_requests != NIL)
-               return true;
-
-       /* Search to see if there's an open request to write this database. */
-       if (list_member_oid(pending_write_requests, databaseid))
-               return true;
-
-       return false;
-}
-
-
-/* ------------------------------------------------------------
- * stats collector message processing functions
- * ------------------------------------------------------------
- */
-
-/*
- * Process stat inquiry requests.
- */
-static void
-pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       elog(DEBUG2, "received inquiry for database %u", msg->databaseid);
-
-       /*
-        * If there's already a write request for this DB, there's nothing to do.
-        *
-        * Note that if a request is found, we return early and skip the below
-        * check for clock skew.  This is okay, since the only way for a DB
-        * request to be present in the list is that we have been here since the
-        * last write round.  It seems sufficient to check for clock skew once per
-        * write round.
-        */
-       if (list_member_oid(pending_write_requests, msg->databaseid))
-               return;
-
-       /*
-        * Check to see if we last wrote this database at a time >= the requested
-        * cutoff time.  If so, this is a stale request that was generated before
-        * we updated the DB file, and we don't need to do so again.
-        *
-        * If the requestor's local clock time is older than stats_timestamp, we
-        * should suspect a clock glitch, ie system time going backwards; though
-        * the more likely explanation is just delayed message receipt.  It is
-        * worth expending a GetCurrentTimestamp call to be sure, since a large
-        * retreat in the system clock reading could otherwise cause us to neglect
-        * to update the stats file for a long time.
-        */
-       dbentry = pgstat_get_db_entry(msg->databaseid, false);
-       if (dbentry == NULL)
-       {
-               /*
-                * We have no data for this DB.  Enter a write request anyway so that
-                * the global stats will get updated.  This is needed to prevent
-                * backend_read_statsfile from waiting for data that we cannot supply,
-                * in the case of a new DB that nobody has yet reported any stats for.
-                * See the behavior of pgstat_read_db_statsfile_timestamp.
-                */
-       }
-       else if (msg->clock_time < dbentry->stats_timestamp)
-       {
-               TimestampTz cur_ts = GetCurrentTimestamp();
-
-               if (cur_ts < dbentry->stats_timestamp)
-               {
-                       /*
-                        * Sure enough, time went backwards.  Force a new stats file write
-                        * to get back in sync; but first, log a complaint.
-                        */
-                       char       *writetime;
-                       char       *mytime;
-
-                       /* Copy because timestamptz_to_str returns a static buffer */
-                       writetime = pstrdup(timestamptz_to_str(dbentry->stats_timestamp));
-                       mytime = pstrdup(timestamptz_to_str(cur_ts));
-                       ereport(LOG,
-                                       (errmsg("stats_timestamp %s is later than collector's time %s for database %u",
-                                                       writetime, mytime, dbentry->databaseid)));
-                       pfree(writetime);
-                       pfree(mytime);
-               }
-               else
-               {
-                       /*
-                        * Nope, it's just an old request.  Assuming msg's clock_time is
-                        * >= its cutoff_time, it must be stale, so we can ignore it.
-                        */
-                       return;
-               }
-       }
-       else if (msg->cutoff_time <= dbentry->stats_timestamp)
-       {
-               /* Stale request, ignore it */
-               return;
-       }
-
-       /*
-        * We need to write this DB, so create a request.
-        */
-       pending_write_requests = lappend_oid(pending_write_requests,
-                                                                                msg->databaseid);
-}
-
-/*
- * Count what the backend has done.
- */
-static void
-pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatTabEntry *tabentry;
-       int                     i;
-       bool            found;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       /*
-        * Update database-wide stats.
-        */
-       dbentry->n_xact_commit += (PgStat_Counter) (msg->m_xact_commit);
-       dbentry->n_xact_rollback += (PgStat_Counter) (msg->m_xact_rollback);
-       dbentry->n_block_read_time += msg->m_block_read_time;
-       dbentry->n_block_write_time += msg->m_block_write_time;
-
-       dbentry->total_session_time += msg->m_session_time;
-       dbentry->total_active_time += msg->m_active_time;
-       dbentry->total_idle_in_xact_time += msg->m_idle_in_xact_time;
-
-       /*
-        * Process all table entries in the message.
-        */
-       for (i = 0; i < msg->m_nentries; i++)
-       {
-               PgStat_TableEntry *tabmsg = &(msg->m_entry[i]);
-
-               tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-                                                                                                          (void *) &(tabmsg->t_id),
-                                                                                                          HASH_ENTER, &found);
-
-               if (!found)
-               {
-                       /*
-                        * If it's a new table entry, initialize counters to the values we
-                        * just got.
-                        */
-                       tabentry->numscans = tabmsg->t_counts.t_numscans;
-                       tabentry->tuples_returned = tabmsg->t_counts.t_tuples_returned;
-                       tabentry->tuples_fetched = tabmsg->t_counts.t_tuples_fetched;
-                       tabentry->tuples_inserted = tabmsg->t_counts.t_tuples_inserted;
-                       tabentry->tuples_updated = tabmsg->t_counts.t_tuples_updated;
-                       tabentry->tuples_deleted = tabmsg->t_counts.t_tuples_deleted;
-                       tabentry->tuples_hot_updated = tabmsg->t_counts.t_tuples_hot_updated;
-                       tabentry->n_live_tuples = tabmsg->t_counts.t_delta_live_tuples;
-                       tabentry->n_dead_tuples = tabmsg->t_counts.t_delta_dead_tuples;
-                       tabentry->changes_since_analyze = tabmsg->t_counts.t_changed_tuples;
-                       tabentry->inserts_since_vacuum = tabmsg->t_counts.t_tuples_inserted;
-                       tabentry->blocks_fetched = tabmsg->t_counts.t_blocks_fetched;
-                       tabentry->blocks_hit = tabmsg->t_counts.t_blocks_hit;
-
-                       tabentry->vacuum_timestamp = 0;
-                       tabentry->vacuum_count = 0;
-                       tabentry->autovac_vacuum_timestamp = 0;
-                       tabentry->autovac_vacuum_count = 0;
-                       tabentry->analyze_timestamp = 0;
-                       tabentry->analyze_count = 0;
-                       tabentry->autovac_analyze_timestamp = 0;
-                       tabentry->autovac_analyze_count = 0;
-               }
-               else
-               {
-                       /*
-                        * Otherwise add the values to the existing entry.
-                        */
-                       tabentry->numscans += tabmsg->t_counts.t_numscans;
-                       tabentry->tuples_returned += tabmsg->t_counts.t_tuples_returned;
-                       tabentry->tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-                       tabentry->tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-                       tabentry->tuples_updated += tabmsg->t_counts.t_tuples_updated;
-                       tabentry->tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-                       tabentry->tuples_hot_updated += tabmsg->t_counts.t_tuples_hot_updated;
-
-                       /*
-                        * If table was truncated/dropped, first reset the live/dead
-                        * counters.
-                        */
-                       if (tabmsg->t_counts.t_truncdropped)
-                       {
-                               tabentry->n_live_tuples = 0;
-                               tabentry->n_dead_tuples = 0;
-                               tabentry->inserts_since_vacuum = 0;
-                       }
-                       tabentry->n_live_tuples += tabmsg->t_counts.t_delta_live_tuples;
-                       tabentry->n_dead_tuples += tabmsg->t_counts.t_delta_dead_tuples;
-                       tabentry->changes_since_analyze += tabmsg->t_counts.t_changed_tuples;
-                       tabentry->inserts_since_vacuum += tabmsg->t_counts.t_tuples_inserted;
-                       tabentry->blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-                       tabentry->blocks_hit += tabmsg->t_counts.t_blocks_hit;
-               }
-
-               /* Clamp n_live_tuples in case of negative delta_live_tuples */
-               tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
-               /* Likewise for n_dead_tuples */
-               tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);
-
-               /*
-                * Add per-table stats to the per-database entry, too.
-                */
-               dbentry->n_tuples_returned += tabmsg->t_counts.t_tuples_returned;
-               dbentry->n_tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-               dbentry->n_tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-               dbentry->n_tuples_updated += tabmsg->t_counts.t_tuples_updated;
-               dbentry->n_tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-               dbentry->n_blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-               dbentry->n_blocks_hit += tabmsg->t_counts.t_blocks_hit;
-       }
-}
-
-/*
- * Arrange for dead table removal.
- */
-static void
-pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-       int                     i;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-       /*
-        * No need to purge if we don't even know the database.
-        */
-       if (!dbentry || !dbentry->tables)
-               return;
-
-       /*
-        * Process all table entries in the message.
-        */
-       for (i = 0; i < msg->m_nentries; i++)
-       {
-               /* Remove from hashtable if present; we don't care if it's not. */
-               (void) hash_search(dbentry->tables,
-                                                  (void *) &(msg->m_tableid[i]),
-                                                  HASH_REMOVE, NULL);
-       }
-}
-
-/*
- * Arrange for dead database removal
- */
-static void
-pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len)
-{
-       Oid                     dbid = msg->m_databaseid;
-       PgStat_StatDBEntry *dbentry;
-
-       /*
-        * Lookup the database in the hashtable.
-        */
-       dbentry = pgstat_get_db_entry(dbid, false);
-
-       /*
-        * If found, remove it (along with the db statfile).
-        */
-       if (dbentry)
-       {
-               char            statfile[MAXPGPATH];
-
-               get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
-
-               elog(DEBUG2, "removing stats file \"%s\"", statfile);
-               unlink(statfile);
-
-               if (dbentry->tables != NULL)
-                       hash_destroy(dbentry->tables);
-               if (dbentry->functions != NULL)
-                       hash_destroy(dbentry->functions);
-
-               if (hash_search(pgStatDBHash,
-                                               (void *) &dbid,
-                                               HASH_REMOVE, NULL) == NULL)
-                       ereport(ERROR,
-                                       (errmsg("database hash table corrupted during cleanup --- abort")));
-       }
-}
-
-/*
- * Reset the statistics for the specified database.
- */
-static void
-pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       /*
-        * Lookup the database in the hashtable.  Nothing to do if not there.
-        */
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-       if (!dbentry)
-               return;
-
-       /*
-        * We simply throw away all the database's table entries by recreating a
-        * new hash table for them.
-        */
-       if (dbentry->tables != NULL)
-               hash_destroy(dbentry->tables);
-       if (dbentry->functions != NULL)
-               hash_destroy(dbentry->functions);
-
-       dbentry->tables = NULL;
-       dbentry->functions = NULL;
-
-       /*
-        * Reset database-level stats, too.  This creates empty hash tables for
-        * tables and functions.
-        */
-       reset_dbentry_counters(dbentry);
-}
-
-/*
- * Reset some shared statistics of the cluster.
- */
-static void
-pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
-{
-       if (msg->m_resettarget == PGSTAT_KIND_BGWRITER ||
-               msg->m_resettarget == PGSTAT_KIND_CHECKPOINTER)
-       {
-               /*
-                * Reset the global, bgwriter and checkpointer statistics for the
-                * cluster.
-                */
-               memset(&globalStats, 0, sizeof(globalStats));
-               globalStats.bgwriter.stat_reset_timestamp = GetCurrentTimestamp();
-       }
-       else if (msg->m_resettarget == PGSTAT_KIND_ARCHIVER)
-       {
-               /* Reset the archiver statistics for the cluster. */
-               memset(&archiverStats, 0, sizeof(archiverStats));
-               archiverStats.stat_reset_timestamp = GetCurrentTimestamp();
-       }
-       else if (msg->m_resettarget == PGSTAT_KIND_WAL)
-       {
-               /* Reset the WAL statistics for the cluster. */
-               memset(&walStats, 0, sizeof(walStats));
-               walStats.stat_reset_timestamp = GetCurrentTimestamp();
-       }
-
-       /*
-        * Presumably the sender of this message validated the target, don't
-        * complain here if it's not valid
-        */
-}
-
-/*
- * Reset a statistics for a single object, which may be of current
- * database or shared across all databases in the cluster.
- */
-static void
-pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       if (IsSharedRelation(msg->m_objectid))
-               dbentry = pgstat_get_db_entry(InvalidOid, false);
-       else
-               dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-       if (!dbentry)
-               return;
-
-       /* Set the reset timestamp for the whole database */
-       dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-
-       /* Remove object if it exists, ignore it if not */
-       if (msg->m_resettype == PGSTAT_KIND_RELATION)
-               (void) hash_search(dbentry->tables, (void *) &(msg->m_objectid),
-                                                  HASH_REMOVE, NULL);
-       else if (msg->m_resettype == PGSTAT_KIND_FUNCTION)
-               (void) hash_search(dbentry->functions, (void *) &(msg->m_objectid),
-                                                  HASH_REMOVE, NULL);
-}
-
-/*
- * Reset some SLRU statistics of the cluster.
- */
-static void
-pgstat_recv_resetslrucounter(PgStat_MsgResetslrucounter *msg, int len)
-{
-       int                     i;
-       TimestampTz ts = GetCurrentTimestamp();
-
-       for (i = 0; i < SLRU_NUM_ELEMENTS; i++)
-       {
-               /* reset entry with the given index, or all entries (index is -1) */
-               if ((msg->m_index == -1) || (msg->m_index == i))
-               {
-                       memset(&slruStats[i], 0, sizeof(slruStats[i]));
-                       slruStats[i].stat_reset_timestamp = ts;
-               }
-       }
-}
-
-/*
- * Reset some replication slot statistics of the cluster.
- */
-static void
-pgstat_recv_resetreplslotcounter(PgStat_MsgResetreplslotcounter *msg,
-                                                                int len)
-{
-       PgStat_StatReplSlotEntry *slotent;
-       TimestampTz ts;
-
-       /* Return if we don't have replication slot statistics */
-       if (replSlotStatHash == NULL)
-               return;
-
-       ts = GetCurrentTimestamp();
-       if (msg->clearall)
-       {
-               HASH_SEQ_STATUS sstat;
-
-               hash_seq_init(&sstat, replSlotStatHash);
-               while ((slotent = (PgStat_StatReplSlotEntry *) hash_seq_search(&sstat)) != NULL)
-                       pgstat_reset_replslot_entry(slotent, ts);
-       }
-       else
-       {
-               /* Get the slot statistics to reset */
-               slotent = pgstat_get_replslot_entry(msg->m_slotname, false);
-
-               /*
-                * Nothing to do if the given slot entry is not found.  This could
-                * happen when the slot with the given name is removed and the
-                * corresponding statistics entry is also removed before receiving the
-                * reset message.
-                */
-               if (!slotent)
-                       return;
-
-               /* Reset the stats for the requested replication slot */
-               pgstat_reset_replslot_entry(slotent, ts);
-       }
-}
-
-/*
- * Reset some subscription statistics of the cluster.
- */
-static void
-pgstat_recv_resetsubcounter(PgStat_MsgResetsubcounter *msg, int len)
-{
-       PgStat_StatSubEntry *subentry;
-       TimestampTz ts;
-
-       /* Return if we don't have replication subscription statistics */
-       if (subscriptionStatHash == NULL)
-               return;
-
-       ts = GetCurrentTimestamp();
-       if (!OidIsValid(msg->m_subid))
-       {
-               HASH_SEQ_STATUS sstat;
-
-               /* Clear all subscription counters */
-               hash_seq_init(&sstat, subscriptionStatHash);
-               while ((subentry = (PgStat_StatSubEntry *) hash_seq_search(&sstat)) != NULL)
-                       pgstat_reset_subscription(subentry, ts);
-       }
-       else
-       {
-               /* Get the subscription statistics to reset */
-               subentry = pgstat_get_subscription_entry(msg->m_subid, false);
-
-               /*
-                * Nothing to do if the given subscription entry is not found.  This
-                * could happen when the subscription with the subid is removed and
-                * the corresponding statistics entry is also removed before receiving
-                * the reset message.
-                */
-               if (!subentry)
-                       return;
-
-               /* Reset the stats for the requested subscription */
-               pgstat_reset_subscription(subentry, ts);
-       }
-}
-
-/*
- * Process an autovacuum signaling message.
- */
-static void
-pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       /*
-        * Store the last autovacuum time in the database's hashtable entry.
-        */
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       dbentry->last_autovac_time = msg->m_start_time;
-}
-
-/*
- * Process a VACUUM message.
- */
-static void
-pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatTabEntry *tabentry;
-
-       /*
-        * Store the data in the table's hashtable entry.
-        */
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-       tabentry->n_live_tuples = msg->m_live_tuples;
-       tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-       /*
-        * It is quite possible that a non-aggressive VACUUM ended up skipping
-        * various pages, however, we'll zero the insert counter here regardless.
-        * It's currently used only to track when we need to perform an "insert"
-        * autovacuum, which are mainly intended to freeze newly inserted tuples.
-        * Zeroing this may just mean we'll not try to vacuum the table again
-        * until enough tuples have been inserted to trigger another insert
-        * autovacuum.  An anti-wraparound autovacuum will catch any persistent
-        * stragglers.
-        */
-       tabentry->inserts_since_vacuum = 0;
-
-       if (msg->m_autovacuum)
-       {
-               tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
-               tabentry->autovac_vacuum_count++;
-       }
-       else
-       {
-               tabentry->vacuum_timestamp = msg->m_vacuumtime;
-               tabentry->vacuum_count++;
-       }
-}
-
-/*
- * Process an ANALYZE message.
- */
-static void
-pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatTabEntry *tabentry;
-
-       /*
-        * Store the data in the table's hashtable entry.
-        */
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-       tabentry->n_live_tuples = msg->m_live_tuples;
-       tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-       /*
-        * If commanded, reset changes_since_analyze to zero.  This forgets any
-        * changes that were committed while the ANALYZE was in progress, but we
-        * have no good way to estimate how many of those there were.
-        */
-       if (msg->m_resetcounter)
-               tabentry->changes_since_analyze = 0;
-
-       if (msg->m_autovacuum)
-       {
-               tabentry->autovac_analyze_timestamp = msg->m_analyzetime;
-               tabentry->autovac_analyze_count++;
-       }
-       else
-       {
-               tabentry->analyze_timestamp = msg->m_analyzetime;
-               tabentry->analyze_count++;
-       }
-}
-
-/*
- * Process a ARCHIVER message.
- */
-static void
-pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len)
-{
-       if (msg->m_failed)
-       {
-               /* Failed archival attempt */
-               ++archiverStats.failed_count;
-               memcpy(archiverStats.last_failed_wal, msg->m_xlog,
-                          sizeof(archiverStats.last_failed_wal));
-               archiverStats.last_failed_timestamp = msg->m_timestamp;
-       }
-       else
-       {
-               /* Successful archival operation */
-               ++archiverStats.archived_count;
-               memcpy(archiverStats.last_archived_wal, msg->m_xlog,
-                          sizeof(archiverStats.last_archived_wal));
-               archiverStats.last_archived_timestamp = msg->m_timestamp;
-       }
-}
-
-/*
- * Process a BGWRITER message.
- */
-static void
-pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
-{
-       globalStats.bgwriter.buf_written_clean += msg->m_buf_written_clean;
-       globalStats.bgwriter.maxwritten_clean += msg->m_maxwritten_clean;
-       globalStats.bgwriter.buf_alloc += msg->m_buf_alloc;
-}
-
-/*
- * Process a CHECKPOINTER message.
- */
-static void
-pgstat_recv_checkpointer(PgStat_MsgCheckpointer *msg, int len)
-{
-       globalStats.checkpointer.timed_checkpoints += msg->m_timed_checkpoints;
-       globalStats.checkpointer.requested_checkpoints += msg->m_requested_checkpoints;
-       globalStats.checkpointer.checkpoint_write_time += msg->m_checkpoint_write_time;
-       globalStats.checkpointer.checkpoint_sync_time += msg->m_checkpoint_sync_time;
-       globalStats.checkpointer.buf_written_checkpoints += msg->m_buf_written_checkpoints;
-       globalStats.checkpointer.buf_written_backend += msg->m_buf_written_backend;
-       globalStats.checkpointer.buf_fsync_backend += msg->m_buf_fsync_backend;
-}
-
-/*
- * Process a WAL message.
- */
-static void
-pgstat_recv_wal(PgStat_MsgWal *msg, int len)
-{
-       walStats.wal_records += msg->m_wal_records;
-       walStats.wal_fpi += msg->m_wal_fpi;
-       walStats.wal_bytes += msg->m_wal_bytes;
-       walStats.wal_buffers_full += msg->m_wal_buffers_full;
-       walStats.wal_write += msg->m_wal_write;
-       walStats.wal_sync += msg->m_wal_sync;
-       walStats.wal_write_time += msg->m_wal_write_time;
-       walStats.wal_sync_time += msg->m_wal_sync_time;
-}
-
-/*
- * Process a SLRU message.
- */
-static void
-pgstat_recv_slru(PgStat_MsgSLRU *msg, int len)
-{
-       slruStats[msg->m_index].blocks_zeroed += msg->m_blocks_zeroed;
-       slruStats[msg->m_index].blocks_hit += msg->m_blocks_hit;
-       slruStats[msg->m_index].blocks_read += msg->m_blocks_read;
-       slruStats[msg->m_index].blocks_written += msg->m_blocks_written;
-       slruStats[msg->m_index].blocks_exists += msg->m_blocks_exists;
-       slruStats[msg->m_index].flush += msg->m_flush;
-       slruStats[msg->m_index].truncate += msg->m_truncate;
-}
-
-/*
- * Process a RECOVERYCONFLICT message.
- */
-static void
-pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       switch (msg->m_reason)
-       {
-               case PROCSIG_RECOVERY_CONFLICT_DATABASE:
-
-                       /*
-                        * Since we drop the information about the database as soon as it
-                        * replicates, there is no point in counting these conflicts.
-                        */
-                       break;
-               case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
-                       dbentry->n_conflict_tablespace++;
-                       break;
-               case PROCSIG_RECOVERY_CONFLICT_LOCK:
-                       dbentry->n_conflict_lock++;
-                       break;
-               case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
-                       dbentry->n_conflict_snapshot++;
-                       break;
-               case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
-                       dbentry->n_conflict_bufferpin++;
-                       break;
-               case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
-                       dbentry->n_conflict_startup_deadlock++;
-                       break;
-       }
-}
-
-/*
- * Process a DEADLOCK message.
- */
-static void
-pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       dbentry->n_deadlocks++;
-}
-
-/*
- * Process a CHECKSUMFAILURE message.
- */
-static void
-pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       dbentry->n_checksum_failures += msg->m_failurecount;
-       dbentry->last_checksum_failure = msg->m_failure_time;
-}
-
-/*
- * Process a REPLSLOT message.
- */
-static void
-pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)
-{
-       if (msg->m_drop)
-       {
-               Assert(!msg->m_create);
-
-               /* Remove the replication slot statistics with the given name */
-               if (replSlotStatHash != NULL)
-                       (void) hash_search(replSlotStatHash,
-                                                          (void *) &(msg->m_slotname),
-                                                          HASH_REMOVE,
-                                                          NULL);
-       }
-       else
-       {
-               PgStat_StatReplSlotEntry *slotent;
-
-               slotent = pgstat_get_replslot_entry(msg->m_slotname, true);
-               Assert(slotent);
-
-               if (msg->m_create)
-               {
-                       /*
-                        * If the message for dropping the slot with the same name gets
-                        * lost, slotent has stats for the old slot. So we initialize all
-                        * counters at slot creation.
-                        */
-                       pgstat_reset_replslot_entry(slotent, 0);
-               }
-               else
-               {
-                       /* Update the replication slot statistics */
-                       slotent->spill_txns += msg->m_spill_txns;
-                       slotent->spill_count += msg->m_spill_count;
-                       slotent->spill_bytes += msg->m_spill_bytes;
-                       slotent->stream_txns += msg->m_stream_txns;
-                       slotent->stream_count += msg->m_stream_count;
-                       slotent->stream_bytes += msg->m_stream_bytes;
-                       slotent->total_txns += msg->m_total_txns;
-                       slotent->total_bytes += msg->m_total_bytes;
-               }
-       }
-}
-
-/*
- * Process a CONNECT message.
- */
-static void
-pgstat_recv_connect(PgStat_MsgConnect *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-       dbentry->n_sessions++;
-}
-
-/*
- * Process a DISCONNECT message.
- */
-static void
-pgstat_recv_disconnect(PgStat_MsgDisconnect *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       switch (msg->m_cause)
-       {
-               case DISCONNECT_NOT_YET:
-               case DISCONNECT_NORMAL:
-                       /* we don't collect these */
-                       break;
-               case DISCONNECT_CLIENT_EOF:
-                       dbentry->n_sessions_abandoned++;
-                       break;
-               case DISCONNECT_FATAL:
-                       dbentry->n_sessions_fatal++;
-                       break;
-               case DISCONNECT_KILLED:
-                       dbentry->n_sessions_killed++;
-                       break;
-       }
-}
-
-/*
- * Process a TEMPFILE message.
- */
-static void
-pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       dbentry->n_temp_bytes += msg->m_filesize;
-       dbentry->n_temp_files += 1;
-}
-
-/*
- * Count what the backend has done.
- */
-static void
-pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len)
-{
-       PgStat_FunctionEntry *funcmsg = &(msg->m_entry[0]);
-       PgStat_StatDBEntry *dbentry;
-       PgStat_StatFuncEntry *funcentry;
-       int                     i;
-       bool            found;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-       /*
-        * Process all function entries in the message.
-        */
-       for (i = 0; i < msg->m_nentries; i++, funcmsg++)
-       {
-               funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-                                                                                                                (void *) &(funcmsg->f_id),
-                                                                                                                HASH_ENTER, &found);
-
-               if (!found)
-               {
-                       /*
-                        * If it's a new function entry, initialize counters to the values
-                        * we just got.
-                        */
-                       funcentry->f_numcalls = funcmsg->f_numcalls;
-                       funcentry->f_total_time = funcmsg->f_total_time;
-                       funcentry->f_self_time = funcmsg->f_self_time;
-               }
-               else
-               {
-                       /*
-                        * Otherwise add the values to the existing entry.
-                        */
-                       funcentry->f_numcalls += funcmsg->f_numcalls;
-                       funcentry->f_total_time += funcmsg->f_total_time;
-                       funcentry->f_self_time += funcmsg->f_self_time;
-               }
-       }
-}
-
-/*
- * Arrange for dead function removal.
- */
-static void
-pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len)
-{
-       PgStat_StatDBEntry *dbentry;
-       int                     i;
-
-       dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-       /*
-        * No need to purge if we don't even know the database.
-        */
-       if (!dbentry || !dbentry->functions)
-               return;
-
-       /*
-        * Process all function entries in the message.
-        */
-       for (i = 0; i < msg->m_nentries; i++)
-       {
-               /* Remove from hashtable if present; we don't care if it's not. */
-               (void) hash_search(dbentry->functions,
-                                                  (void *) &(msg->m_functionid[i]),
-                                                  HASH_REMOVE, NULL);
-       }
-}
-
-/*
- * Process a SUBSCRIPTIONDROP message.
- */
-static void
-pgstat_recv_subscription_drop(PgStat_MsgSubscriptionDrop *msg, int len)
-{
-       /* Return if we don't have replication subscription statistics */
-       if (subscriptionStatHash == NULL)
-               return;
-
-       /* Remove from hashtable if present; we don't care if it's not */
-       (void) hash_search(subscriptionStatHash, (void *) &(msg->m_subid),
-                                          HASH_REMOVE, NULL);
-}
-
-/*
- * Process a SUBSCRIPTIONERROR message.
- */
-static void
-pgstat_recv_subscription_error(PgStat_MsgSubscriptionError *msg, int len)
-{
-       PgStat_StatSubEntry *subentry;
-
-       /* Get the subscription stats */
-       subentry = pgstat_get_subscription_entry(msg->m_subid, true);
-       Assert(subentry);
-
-       if (msg->m_is_apply_error)
-               subentry->apply_error_count++;
-       else
-               subentry->sync_error_count++;
+       /* and drop variable-numbered ones */
+       pgstat_drop_all_entries();
 }
index 9f7034df112a0ae012db4041de566a5741bd466a..d5551e0af68086c95ed24fc40b30d03a3f92654f 100644 (file)
@@ -255,7 +255,6 @@ static pid_t StartupPID = 0,
                        WalReceiverPID = 0,
                        AutoVacPID = 0,
                        PgArchPID = 0,
-                       PgStatPID = 0,
                        SysLoggerPID = 0;
 
 /* Startup process's status */
@@ -510,7 +509,6 @@ typedef struct
        PGPROC     *AuxiliaryProcs;
        PGPROC     *PreparedXactProcs;
        PMSignalData *PMSignalState;
-       InheritableSocket pgStatSock;
        pid_t           PostmasterPid;
        TimestampTz PgStartTime;
        TimestampTz PgReloadTime;
@@ -645,9 +643,8 @@ PostmasterMain(int argc, char *argv[])
         * CAUTION: when changing this list, check for side-effects on the signal
         * handling setup of child processes.  See tcop/postgres.c,
         * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c,
-        * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/pgstat.c,
-        * postmaster/syslogger.c, postmaster/bgworker.c and
-        * postmaster/checkpointer.c.
+        * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/syslogger.c,
+        * postmaster/bgworker.c and postmaster/checkpointer.c.
         */
        pqinitmask();
        PG_SETMASK(&BlockSig);
@@ -1384,12 +1381,6 @@ PostmasterMain(int argc, char *argv[])
         */
        RemovePgTempFiles();
 
-       /*
-        * Initialize stats collection subsystem (this does NOT start the
-        * collector process!)
-        */
-       pgstat_init();
-
        /*
         * Initialize the autovacuum subsystem (again, no process start yet)
         */
@@ -1845,11 +1836,6 @@ ServerLoop(void)
                                start_autovac_launcher = false; /* signal processed */
                }
 
-               /* If we have lost the stats collector, try to start a new one */
-               if (PgStatPID == 0 &&
-                       (pmState == PM_RUN || pmState == PM_HOT_STANDBY))
-                       PgStatPID = pgstat_start();
-
                /* If we have lost the archiver, try to start a new one. */
                if (PgArchPID == 0 && PgArchStartupAllowed())
                        PgArchPID = StartArchiver();
@@ -2772,8 +2758,6 @@ SIGHUP_handler(SIGNAL_ARGS)
                        signal_child(PgArchPID, SIGHUP);
                if (SysLoggerPID != 0)
                        signal_child(SysLoggerPID, SIGHUP);
-               if (PgStatPID != 0)
-                       signal_child(PgStatPID, SIGHUP);
 
                /* Reload authentication config files too */
                if (!load_hba())
@@ -3097,8 +3081,6 @@ reaper(SIGNAL_ARGS)
                                AutoVacPID = StartAutoVacLauncher();
                        if (PgArchStartupAllowed() && PgArchPID == 0)
                                PgArchPID = StartArchiver();
-                       if (PgStatPID == 0)
-                               PgStatPID = pgstat_start();
 
                        /* workers may be scheduled to start now */
                        maybe_start_bgworkers();
@@ -3165,13 +3147,6 @@ reaper(SIGNAL_ARGS)
                                SignalChildren(SIGUSR2);
 
                                pmState = PM_SHUTDOWN_2;
-
-                               /*
-                                * We can also shut down the stats collector now; there's
-                                * nothing left for it to do.
-                                */
-                               if (PgStatPID != 0)
-                                       signal_child(PgStatPID, SIGQUIT);
                        }
                        else
                        {
@@ -3250,22 +3225,6 @@ reaper(SIGNAL_ARGS)
                        continue;
                }
 
-               /*
-                * Was it the statistics collector?  If so, just try to start a new
-                * one; no need to force reset of the rest of the system.  (If fail,
-                * we'll try again in future cycles of the main loop.)
-                */
-               if (pid == PgStatPID)
-               {
-                       PgStatPID = 0;
-                       if (!EXIT_STATUS_0(exitstatus))
-                               LogChildExit(LOG, _("statistics collector process"),
-                                                        pid, exitstatus);
-                       if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
-                               PgStatPID = pgstat_start();
-                       continue;
-               }
-
                /* Was it the system logger?  If so, try to start a new one */
                if (pid == SysLoggerPID)
                {
@@ -3707,22 +3666,6 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
                signal_child(PgArchPID, (SendStop ? SIGSTOP : SIGQUIT));
        }
 
-       /*
-        * Force a power-cycle of the pgstat process too.  (This isn't absolutely
-        * necessary, but it seems like a good idea for robustness, and it
-        * simplifies the state-machine logic in the case where a shutdown request
-        * arrives during crash processing.)
-        */
-       if (PgStatPID != 0 && take_action)
-       {
-               ereport(DEBUG2,
-                               (errmsg_internal("sending %s to process %d",
-                                                                "SIGQUIT",
-                                                                (int) PgStatPID)));
-               signal_child(PgStatPID, SIGQUIT);
-               allow_immediate_pgstat_restart();
-       }
-
        /* We do NOT restart the syslogger */
 
        if (Shutdown != ImmediateShutdown)
@@ -3934,12 +3877,10 @@ PostmasterStateMachine(void)
                                        FatalError = true;
                                        pmState = PM_WAIT_DEAD_END;
 
-                                       /* Kill the walsenders, archiver and stats collector too */
+                                       /* Kill the walsenders and archiver too */
                                        SignalChildren(SIGQUIT);
                                        if (PgArchPID != 0)
                                                signal_child(PgArchPID, SIGQUIT);
-                                       if (PgStatPID != 0)
-                                               signal_child(PgStatPID, SIGQUIT);
                                }
                        }
                }
@@ -3963,8 +3904,7 @@ PostmasterStateMachine(void)
        {
                /*
                 * PM_WAIT_DEAD_END state ends when the BackendList is entirely empty
-                * (ie, no dead_end children remain), and the archiver and stats
-                * collector are gone too.
+                * (ie, no dead_end children remain), and the archiver is gone too.
                 *
                 * The reason we wait for those two is to protect them against a new
                 * postmaster starting conflicting subprocesses; this isn't an
@@ -3974,8 +3914,7 @@ PostmasterStateMachine(void)
                 * normal state transition leading up to PM_WAIT_DEAD_END, or during
                 * FatalError processing.
                 */
-               if (dlist_is_empty(&BackendList) &&
-                       PgArchPID == 0 && PgStatPID == 0)
+               if (dlist_is_empty(&BackendList) && PgArchPID == 0)
                {
                        /* These other guys should be dead already */
                        Assert(StartupPID == 0);
@@ -4183,8 +4122,6 @@ TerminateChildren(int signal)
                signal_child(AutoVacPID, signal);
        if (PgArchPID != 0)
                signal_child(PgArchPID, signal);
-       if (PgStatPID != 0)
-               signal_child(PgStatPID, signal);
 }
 
 /*
@@ -5115,12 +5052,6 @@ SubPostmasterMain(int argc, char *argv[])
 
                StartBackgroundWorker();
        }
-       if (strcmp(argv[1], "--forkcol") == 0)
-       {
-               /* Do not want to attach to shared memory */
-
-               PgstatCollectorMain(argc, argv);        /* does not return */
-       }
        if (strcmp(argv[1], "--forklog") == 0)
        {
                /* Do not want to attach to shared memory */
@@ -5224,12 +5155,6 @@ sigusr1_handler(SIGNAL_ARGS)
        if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
                pmState == PM_RECOVERY && Shutdown == NoShutdown)
        {
-               /*
-                * Likewise, start other special children as needed.
-                */
-               Assert(PgStatPID == 0);
-               PgStatPID = pgstat_start();
-
                ereport(LOG,
                                (errmsg("database system is ready to accept read-only connections")));
 
@@ -6145,7 +6070,6 @@ extern slock_t *ShmemLock;
 extern slock_t *ProcStructLock;
 extern PGPROC *AuxiliaryProcs;
 extern PMSignalData *PMSignalState;
-extern pgsocket pgStatSock;
 extern pg_time_t first_syslogger_file_time;
 
 #ifndef WIN32
@@ -6201,8 +6125,6 @@ save_backend_variables(BackendParameters *param, Port *port,
        param->AuxiliaryProcs = AuxiliaryProcs;
        param->PreparedXactProcs = PreparedXactProcs;
        param->PMSignalState = PMSignalState;
-       if (!write_inheritable_socket(&param->pgStatSock, pgStatSock, childPid))
-               return false;
 
        param->PostmasterPid = PostmasterPid;
        param->PgStartTime = PgStartTime;
@@ -6436,7 +6358,6 @@ restore_backend_variables(BackendParameters *param, Port *port)
        AuxiliaryProcs = param->AuxiliaryProcs;
        PreparedXactProcs = param->PreparedXactProcs;
        PMSignalState = param->PMSignalState;
-       read_inheritable_socket(&pgStatSock, &param->pgStatSock);
 
        PostmasterPid = param->PostmasterPid;
        PgStartTime = param->PgStartTime;
@@ -6475,8 +6396,6 @@ restore_backend_variables(BackendParameters *param, Port *port)
        if (postmaster_alive_fds[1] >= 0)
                ReserveExternalFD();
 #endif
-       if (pgStatSock != PGINVALID_SOCKET)
-               ReserveExternalFD();
 }
 
 
index 656ec8f5555b2626c0e600ee82ea110a249e9ede..30e33dace33cf152cf1c9dd285d6cf8dcd6c9806 100644 (file)
@@ -1911,7 +1911,6 @@ UpdateDecodingStats(LogicalDecodingContext *ctx)
                 (long long) rb->totalTxns,
                 (long long) rb->totalBytes);
 
-       namestrcpy(&repSlotStat.slotname, NameStr(ctx->slot->data.name));
        repSlotStat.spill_txns = rb->spillTxns;
        repSlotStat.spill_count = rb->spillCount;
        repSlotStat.spill_bytes = rb->spillBytes;
index 697fb23634cb8335737f25359d96e8efc82f85df..b2cb31eaad71d06fdf4a052a4f8329b5f44d92d3 100644 (file)
@@ -141,7 +141,7 @@ finish_sync_worker(void)
        if (IsTransactionState())
        {
                CommitTransactionCommand();
-               pgstat_report_stat(false);
+               pgstat_report_stat(true);
        }
 
        /* And flush all writes. */
@@ -580,7 +580,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
        if (started_tx)
        {
                CommitTransactionCommand();
-               pgstat_report_stat(false);
+               pgstat_report_stat(true);
        }
 }
 
@@