* still empowered to issue writes if the bgwriter fails to maintain enough
* clean shared buffers.
*
- * The bgwriter is also charged with handling all checkpoints. It will
- * automatically dispatch a checkpoint after a certain amount of time has
- * elapsed since the last one, and it can be signaled to perform requested
- * checkpoints as well. (The GUC parameter that mandates a checkpoint every
- * so many WAL segments is implemented by having backends signal the bgwriter
- * when they fill WAL segments; the bgwriter itself doesn't watch for the
- * condition.)
+ * As of Postgres 9.2 the bgwriter no longer handles checkpoints.
*
* The bgwriter is started by the postmaster as soon as the startup subprocess
* finishes, or as soon as recovery begins if we are doing archive recovery.
* It remains alive until the postmaster commands it to terminate.
- * Normal termination is by SIGUSR2, which instructs the bgwriter to execute
- * a shutdown checkpoint and then exit(0). (All backends must be stopped
- * before SIGUSR2 is issued!) Emergency termination is by SIGQUIT; like any
+ * Normal termination is by SIGUSR2, which instructs the bgwriter to exit(0).
+ * Emergency termination is by SIGQUIT; like any
* backend, the bgwriter will simply abort and exit on SIGQUIT.
*
* If the bgwriter exits unexpectedly, the postmaster treats that the same
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
-#include "replication/syncrep.h"
#include "storage/bufmgr.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "utils/resowner.h"
-/*----------
- * Shared memory area for communication between bgwriter and backends
- *
- * The ckpt counters allow backends to watch for completion of a checkpoint
- * request they send. Here's how it works:
- * * At start of a checkpoint, bgwriter reads (and clears) the request flags
- * and increments ckpt_started, while holding ckpt_lck.
- * * On completion of a checkpoint, bgwriter sets ckpt_done to
- * equal ckpt_started.
- * * On failure of a checkpoint, bgwriter increments ckpt_failed
- * and sets ckpt_done to equal ckpt_started.
- *
- * The algorithm for backends is:
- * 1. Record current values of ckpt_failed and ckpt_started, and
- * set request flags, while holding ckpt_lck.
- * 2. Send signal to request checkpoint.
- * 3. Sleep until ckpt_started changes. Now you know a checkpoint has
- * begun since you started this algorithm (although *not* that it was
- * specifically initiated by your signal), and that it is using your flags.
- * 4. Record new value of ckpt_started.
- * 5. Sleep until ckpt_done >= saved value of ckpt_started. (Use modulo
- * arithmetic here in case counters wrap around.) Now you know a
- * checkpoint has started and completed, but not whether it was
- * successful.
- * 6. If ckpt_failed is different from the originally saved value,
- * assume request failed; otherwise it was definitely successful.
- *
- * ckpt_flags holds the OR of the checkpoint request flags sent by all
- * requesting backends since the last checkpoint start. The flags are
- * chosen so that OR'ing is the correct way to combine multiple requests.
- *
- * num_backend_writes is used to count the number of buffer writes performed
- * by non-bgwriter processes. This counter should be wide enough that it
- * can't overflow during a single bgwriter cycle. num_backend_fsync
- * counts the subset of those writes that also had to do their own fsync,
- * because the background writer failed to absorb their request.
- *
- * The requests array holds fsync requests sent by backends and not yet
- * absorbed by the bgwriter.
- *
- * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
- * the requests fields are protected by BgWriterCommLock.
- *----------
- */
-typedef struct
-{
- RelFileNodeBackend rnode;
- ForkNumber forknum;
- BlockNumber segno; /* see md.c for special values */
- /* might add a real request-type field later; not needed yet */
-} BgWriterRequest;
-
-typedef struct
-{
- pid_t bgwriter_pid; /* PID of bgwriter (0 if not started) */
-
- slock_t ckpt_lck; /* protects all the ckpt_* fields */
-
- int ckpt_started; /* advances when checkpoint starts */
- int ckpt_done; /* advances when checkpoint done */
- int ckpt_failed; /* advances when checkpoint fails */
-
- int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
-
- uint32 num_backend_writes; /* counts non-bgwriter buffer writes */
- uint32 num_backend_fsync; /* counts non-bgwriter fsync calls */
-
- int num_requests; /* current # of requests */
- int max_requests; /* allocated array size */
- BgWriterRequest requests[1]; /* VARIABLE LENGTH ARRAY */
-} BgWriterShmemStruct;
-
-static BgWriterShmemStruct *BgWriterShmem;
-
-/* interval for calling AbsorbFsyncRequests in CheckpointWriteDelay */
-#define WRITES_PER_ABSORB 1000
-
/*
* GUC parameters
*/
int BgWriterDelay = 200;
-int CheckPointTimeout = 300;
-int CheckPointWarning = 30;
-double CheckPointCompletionTarget = 0.5;
/*
* Flags set by interrupt handlers for later service in the main loop.
*/
static volatile sig_atomic_t got_SIGHUP = false;
-static volatile sig_atomic_t checkpoint_requested = false;
static volatile sig_atomic_t shutdown_requested = false;
/*
*/
static bool am_bg_writer = false;
-static bool ckpt_active = false;
-
-/* these values are valid when ckpt_active is true: */
-static pg_time_t ckpt_start_time;
-static XLogRecPtr ckpt_start_recptr;
-static double ckpt_cached_elapsed;
-
-static pg_time_t last_checkpoint_time;
-static pg_time_t last_xlog_switch_time;
-
/* Prototypes for private functions */
-static void CheckArchiveTimeout(void);
static void BgWriterNap(void);
-static bool IsCheckpointOnSchedule(double progress);
-static bool ImmediateCheckpointRequested(void);
-static bool CompactBgwriterRequestQueue(void);
/* Signal handlers */
static void bg_quickdie(SIGNAL_ARGS);
static void BgSigHupHandler(SIGNAL_ARGS);
-static void ReqCheckpointHandler(SIGNAL_ARGS);
static void ReqShutdownHandler(SIGNAL_ARGS);
sigjmp_buf local_sigjmp_buf;
MemoryContext bgwriter_context;
- BgWriterShmem->bgwriter_pid = MyProcPid;
am_bg_writer = true;
/*
* process to participate in ProcSignal signalling.
*/
pqsignal(SIGHUP, BgSigHupHandler); /* set flag to read config file */
- pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
- pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
+ pqsignal(SIGINT, SIG_IGN); /* as of 9.2 no longer requests checkpoint */
+ pqsignal(SIGTERM, ReqShutdownHandler); /* shutdown */
pqsignal(SIGQUIT, bg_quickdie); /* hard crash time */
pqsignal(SIGALRM, SIG_IGN);
pqsignal(SIGPIPE, SIG_IGN);
- pqsignal(SIGUSR1, SIG_IGN); /* reserve for ProcSignal */
- pqsignal(SIGUSR2, ReqShutdownHandler); /* request shutdown */
+ pqsignal(SIGUSR1, SIG_IGN); /* reserve for ProcSignal */
+ pqsignal(SIGUSR2, SIG_IGN); /* request shutdown */
/*
* Reset some signals that are accepted by postmaster but not here
/* We allow SIGQUIT (quickdie) at all times */
sigdelset(&BlockSig, SIGQUIT);
- /*
- * Initialize so that first time-driven event happens at the correct time.
- */
- last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
-
/*
* Create a resource owner to keep track of our resources (currently only
* buffer pins).
AtEOXact_Files();
AtEOXact_HashTables(false);
- /* Warn any waiting backends that the checkpoint failed. */
- if (ckpt_active)
- {
- /* use volatile pointer to prevent code rearrangement */
- volatile BgWriterShmemStruct *bgs = BgWriterShmem;
-
- SpinLockAcquire(&bgs->ckpt_lck);
- bgs->ckpt_failed++;
- bgs->ckpt_done = bgs->ckpt_started;
- SpinLockRelease(&bgs->ckpt_lck);
-
- ckpt_active = false;
- }
-
/*
* Now return to normal top-level context and clear ErrorContext for
* next time.
if (RecoveryInProgress())
ThisTimeLineID = GetRecoveryTargetTLI();
- /* Do this once before starting the loop, then just at SIGHUP time. */
- SyncRepUpdateSyncStandbysDefined();
-
/*
* Loop forever
*/
for (;;)
{
- bool do_checkpoint = false;
- int flags = 0;
- pg_time_t now;
- int elapsed_secs;
-
/*
* Emergency bailout if postmaster has died. This is to avoid the
* necessity for manual cleanup of all postmaster children.
if (!PostmasterIsAlive())
exit(1);
- /*
- * Process any requests or signals received recently.
- */
- AbsorbFsyncRequests();
-
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
/* update global shmem state for sync rep */
- SyncRepUpdateSyncStandbysDefined();
- }
- if (checkpoint_requested)
- {
- checkpoint_requested = false;
- do_checkpoint = true;
- BgWriterStats.m_requested_checkpoints++;
}
if (shutdown_requested)
{
* control back to the sigsetjmp block above
*/
ExitOnAnyError = true;
- /* Close down the database */
- ShutdownXLOG(0, 0);
/* Normal exit from the bgwriter is here */
proc_exit(0); /* done */
}
/*
- * Force a checkpoint if too much time has elapsed since the last one.
- * Note that we count a timed checkpoint in stats only when this
- * occurs without an external request, but we set the CAUSE_TIME flag
- * bit even if there is also an external request.
+ * Do one cycle of dirty-buffer writing.
*/
- now = (pg_time_t) time(NULL);
- elapsed_secs = now - last_checkpoint_time;
- if (elapsed_secs >= CheckPointTimeout)
- {
- if (!do_checkpoint)
- BgWriterStats.m_timed_checkpoints++;
- do_checkpoint = true;
- flags |= CHECKPOINT_CAUSE_TIME;
- }
-
- /*
- * Do a checkpoint if requested, otherwise do one cycle of
- * dirty-buffer writing.
- */
- if (do_checkpoint)
- {
- bool ckpt_performed = false;
- bool do_restartpoint;
-
- /* use volatile pointer to prevent code rearrangement */
- volatile BgWriterShmemStruct *bgs = BgWriterShmem;
-
- /*
- * Check if we should perform a checkpoint or a restartpoint. As a
- * side-effect, RecoveryInProgress() initializes TimeLineID if
- * it's not set yet.
- */
- do_restartpoint = RecoveryInProgress();
-
- /*
- * Atomically fetch the request flags to figure out what kind of a
- * checkpoint we should perform, and increase the started-counter
- * to acknowledge that we've started a new checkpoint.
- */
- SpinLockAcquire(&bgs->ckpt_lck);
- flags |= bgs->ckpt_flags;
- bgs->ckpt_flags = 0;
- bgs->ckpt_started++;
- SpinLockRelease(&bgs->ckpt_lck);
-
- /*
- * The end-of-recovery checkpoint is a real checkpoint that's
- * performed while we're still in recovery.
- */
- if (flags & CHECKPOINT_END_OF_RECOVERY)
- do_restartpoint = false;
-
- /*
- * We will warn if (a) too soon since last checkpoint (whatever
- * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
- * since the last checkpoint start. Note in particular that this
- * implementation will not generate warnings caused by
- * CheckPointTimeout < CheckPointWarning.
- */
- if (!do_restartpoint &&
- (flags & CHECKPOINT_CAUSE_XLOG) &&
- elapsed_secs < CheckPointWarning)
- ereport(LOG,
- (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
- "checkpoints are occurring too frequently (%d seconds apart)",
- elapsed_secs,
- elapsed_secs),
- errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
-
- /*
- * Initialize bgwriter-private variables used during checkpoint.
- */
- ckpt_active = true;
- if (!do_restartpoint)
- ckpt_start_recptr = GetInsertRecPtr();
- ckpt_start_time = now;
- ckpt_cached_elapsed = 0;
-
- /*
- * Do the checkpoint.
- */
- if (!do_restartpoint)
- {
- CreateCheckPoint(flags);
- ckpt_performed = true;
- }
- else
- ckpt_performed = CreateRestartPoint(flags);
-
- /*
- * After any checkpoint, close all smgr files. This is so we
- * won't hang onto smgr references to deleted files indefinitely.
- */
- smgrcloseall();
-
- /*
- * Indicate checkpoint completion to any waiting backends.
- */
- SpinLockAcquire(&bgs->ckpt_lck);
- bgs->ckpt_done = bgs->ckpt_started;
- SpinLockRelease(&bgs->ckpt_lck);
-
- if (ckpt_performed)
- {
- /*
- * Note we record the checkpoint start time not end time as
- * last_checkpoint_time. This is so that time-driven
- * checkpoints happen at a predictable spacing.
- */
- last_checkpoint_time = now;
- }
- else
- {
- /*
- * We were not able to perform the restartpoint (checkpoints
- * throw an ERROR in case of error). Most likely because we
- * have not received any new checkpoint WAL records since the
- * last restartpoint. Try again in 15 s.
- */
- last_checkpoint_time = now - CheckPointTimeout + 15;
- }
-
- ckpt_active = false;
- }
- else
- BgBufferSync();
-
- /* Check for archive_timeout and switch xlog files if necessary. */
- CheckArchiveTimeout();
+ BgBufferSync();
/* Nap for the configured time. */
BgWriterNap();
}
}
-/*
- * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
- *
- * This will switch to a new WAL file and force an archive file write
- * if any activity is recorded in the current WAL file, including just
- * a single checkpoint record.
- */
-static void
-CheckArchiveTimeout(void)
-{
- pg_time_t now;
- pg_time_t last_time;
-
- if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
- return;
-
- now = (pg_time_t) time(NULL);
-
- /* First we do a quick check using possibly-stale local state. */
- if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
- return;
-
- /*
- * Update local state ... note that last_xlog_switch_time is the last time
- * a switch was performed *or requested*.
- */
- last_time = GetLastSegSwitchTime();
-
- last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
-
- /* Now we can do the real check */
- if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
- {
- XLogRecPtr switchpoint;
-
- /* OK, it's time to switch */
- switchpoint = RequestXLogSwitch();
-
- /*
- * If the returned pointer points exactly to a segment boundary,
- * assume nothing happened.
- */
- if ((switchpoint.xrecoff % XLogSegSize) != 0)
- ereport(DEBUG1,
- (errmsg("transaction log switch forced (archive_timeout=%d)",
- XLogArchiveTimeout)));
-
- /*
- * Update state in any case, so we don't retry constantly when the
- * system is idle.
- */
- last_xlog_switch_time = now;
- }
-}
-
/*
* BgWriterNap -- Nap for the configured time or until a signal is received.
*/
* respond reasonably promptly when someone signals us, break down the
* sleep into 1-second increments, and check for interrupts after each
* nap.
- *
- * We absorb pending requests after each short sleep.
*/
- if (bgwriter_lru_maxpages > 0 || ckpt_active)
+ if (bgwriter_lru_maxpages > 0)
udelay = BgWriterDelay * 1000L;
- else if (XLogArchiveTimeout > 0)
- udelay = 1000000L; /* One second */
else
udelay = 10000000L; /* Ten seconds */
while (udelay > 999999L)
{
- if (got_SIGHUP || shutdown_requested ||
- (ckpt_active ? ImmediateCheckpointRequested() : checkpoint_requested))
+ if (got_SIGHUP || shutdown_requested)
break;
pg_usleep(1000000L);
- AbsorbFsyncRequests();
udelay -= 1000000L;
}
- if (!(got_SIGHUP || shutdown_requested ||
- (ckpt_active ? ImmediateCheckpointRequested() : checkpoint_requested)))
+ if (!(got_SIGHUP || shutdown_requested))
pg_usleep(udelay);
}
-/*
- * Returns true if an immediate checkpoint request is pending. (Note that
- * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
- * there is one pending behind it.)
- */
-static bool
-ImmediateCheckpointRequested(void)
-{
- if (checkpoint_requested)
- {
- volatile BgWriterShmemStruct *bgs = BgWriterShmem;
-
- /*
- * We don't need to acquire the ckpt_lck in this case because we're
- * only looking at a single flag bit.
- */
- if (bgs->ckpt_flags & CHECKPOINT_IMMEDIATE)
- return true;
- }
- return false;
-}
-
-/*
- * CheckpointWriteDelay -- yield control to bgwriter during a checkpoint
- *
- * This function is called after each page write performed by BufferSync().
- * It is responsible for keeping the bgwriter's normal activities in
- * progress during a long checkpoint, and for throttling BufferSync()'s
- * write rate to hit checkpoint_completion_target.
- *
- * The checkpoint request flags should be passed in; currently the only one
- * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
- *
- * 'progress' is an estimate of how much of the work has been done, as a
- * fraction between 0.0 meaning none, and 1.0 meaning all done.
- */
-void
-CheckpointWriteDelay(int flags, double progress)
-{
- static int absorb_counter = WRITES_PER_ABSORB;
-
- /* Do nothing if checkpoint is being executed by non-bgwriter process */
- if (!am_bg_writer)
- return;
-
- /*
- * Perform the usual bgwriter duties and take a nap, unless we're behind
- * schedule, in which case we just try to catch up as quickly as possible.
- */
- if (!(flags & CHECKPOINT_IMMEDIATE) &&
- !shutdown_requested &&
- !ImmediateCheckpointRequested() &&
- IsCheckpointOnSchedule(progress))
- {
- if (got_SIGHUP)
- {
- got_SIGHUP = false;
- ProcessConfigFile(PGC_SIGHUP);
- /* update global shmem state for sync rep */
- SyncRepUpdateSyncStandbysDefined();
- }
-
- AbsorbFsyncRequests();
- absorb_counter = WRITES_PER_ABSORB;
-
- BgBufferSync();
- CheckArchiveTimeout();
- BgWriterNap();
- }
- else if (--absorb_counter <= 0)
- {
- /*
- * Absorb pending fsync requests after each WRITES_PER_ABSORB write
- * operations even when we don't sleep, to prevent overflow of the
- * fsync request queue.
- */
- AbsorbFsyncRequests();
- absorb_counter = WRITES_PER_ABSORB;
- }
-}
-
-/*
- * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
- * in time?
- *
- * Compares the current progress against the time/segments elapsed since last
- * checkpoint, and returns true if the progress we've made this far is greater
- * than the elapsed time/segments.
- */
-static bool
-IsCheckpointOnSchedule(double progress)
-{
- XLogRecPtr recptr;
- struct timeval now;
- double elapsed_xlogs,
- elapsed_time;
-
- Assert(ckpt_active);
-
- /* Scale progress according to checkpoint_completion_target. */
- progress *= CheckPointCompletionTarget;
-
- /*
- * Check against the cached value first. Only do the more expensive
- * calculations once we reach the target previously calculated. Since
- * neither time or WAL insert pointer moves backwards, a freshly
- * calculated value can only be greater than or equal to the cached value.
- */
- if (progress < ckpt_cached_elapsed)
- return false;
-
- /*
- * Check progress against WAL segments written and checkpoint_segments.
- *
- * We compare the current WAL insert location against the location
- * computed before calling CreateCheckPoint. The code in XLogInsert that
- * actually triggers a checkpoint when checkpoint_segments is exceeded
- * compares against RedoRecptr, so this is not completely accurate.
- * However, it's good enough for our purposes, we're only calculating an
- * estimate anyway.
- */
- if (!RecoveryInProgress())
- {
- recptr = GetInsertRecPtr();
- elapsed_xlogs =
- (((double) (int32) (recptr.xlogid - ckpt_start_recptr.xlogid)) * XLogSegsPerFile +
- ((double) recptr.xrecoff - (double) ckpt_start_recptr.xrecoff) / XLogSegSize) /
- CheckPointSegments;
-
- if (progress < elapsed_xlogs)
- {
- ckpt_cached_elapsed = elapsed_xlogs;
- return false;
- }
- }
-
- /*
- * Check progress against time elapsed and checkpoint_timeout.
- */
- gettimeofday(&now, NULL);
- elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
- now.tv_usec / 1000000.0) / CheckPointTimeout;
-
- if (progress < elapsed_time)
- {
- ckpt_cached_elapsed = elapsed_time;
- return false;
- }
-
- /* It looks like we're on schedule. */
- return true;
-}
-
-
/* --------------------------------
* signal handler routines
* --------------------------------
got_SIGHUP = true;
}
-/* SIGINT: set flag to run a normal checkpoint right away */
-static void
-ReqCheckpointHandler(SIGNAL_ARGS)
-{
- checkpoint_requested = true;
-}
-
/* SIGUSR2: set flag to run a shutdown checkpoint and exit */
static void
ReqShutdownHandler(SIGNAL_ARGS)
{
shutdown_requested = true;
}
-
-
-/* --------------------------------
- * communication with backends
- * --------------------------------
- */
-
-/*
- * BgWriterShmemSize
- * Compute space needed for bgwriter-related shared memory
- */
-Size
-BgWriterShmemSize(void)
-{
- Size size;
-
- /*
- * Currently, the size of the requests[] array is arbitrarily set equal to
- * NBuffers. This may prove too large or small ...
- */
- size = offsetof(BgWriterShmemStruct, requests);
- size = add_size(size, mul_size(NBuffers, sizeof(BgWriterRequest)));
-
- return size;
-}
-
-/*
- * BgWriterShmemInit
- * Allocate and initialize bgwriter-related shared memory
- */
-void
-BgWriterShmemInit(void)
-{
- bool found;
-
- BgWriterShmem = (BgWriterShmemStruct *)
- ShmemInitStruct("Background Writer Data",
- BgWriterShmemSize(),
- &found);
-
- if (!found)
- {
- /* First time through, so initialize */
- MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct));
- SpinLockInit(&BgWriterShmem->ckpt_lck);
- BgWriterShmem->max_requests = NBuffers;
- }
-}
-
-/*
- * RequestCheckpoint
- * Called in backend processes to request a checkpoint
- *
- * flags is a bitwise OR of the following:
- * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
- * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
- * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
- * ignoring checkpoint_completion_target parameter.
- * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured
- * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
- * CHECKPOINT_END_OF_RECOVERY).
- * CHECKPOINT_WAIT: wait for completion before returning (otherwise,
- * just signal bgwriter to do it, and return).
- * CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
- * (This affects logging, and in particular enables CheckPointWarning.)
- */
-void
-RequestCheckpoint(int flags)
-{
- /* use volatile pointer to prevent code rearrangement */
- volatile BgWriterShmemStruct *bgs = BgWriterShmem;
- int ntries;
- int old_failed,
- old_started;
-
- /*
- * If in a standalone backend, just do it ourselves.
- */
- if (!IsPostmasterEnvironment)
- {
- /*
- * There's no point in doing slow checkpoints in a standalone backend,
- * because there's no other backends the checkpoint could disrupt.
- */
- CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);
-
- /*
- * After any checkpoint, close all smgr files. This is so we won't
- * hang onto smgr references to deleted files indefinitely.
- */
- smgrcloseall();
-
- return;
- }
-
- /*
- * Atomically set the request flags, and take a snapshot of the counters.
- * When we see ckpt_started > old_started, we know the flags we set here
- * have been seen by bgwriter.
- *
- * Note that we OR the flags with any existing flags, to avoid overriding
- * a "stronger" request by another backend. The flag senses must be
- * chosen to make this work!
- */
- SpinLockAcquire(&bgs->ckpt_lck);
-
- old_failed = bgs->ckpt_failed;
- old_started = bgs->ckpt_started;
- bgs->ckpt_flags |= flags;
-
- SpinLockRelease(&bgs->ckpt_lck);
-
- /*
- * Send signal to request checkpoint. It's possible that the bgwriter
- * hasn't started yet, or is in process of restarting, so we will retry a
- * few times if needed. Also, if not told to wait for the checkpoint to
- * occur, we consider failure to send the signal to be nonfatal and merely
- * LOG it.
- */
- for (ntries = 0;; ntries++)
- {
- if (BgWriterShmem->bgwriter_pid == 0)
- {
- if (ntries >= 20) /* max wait 2.0 sec */
- {
- elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
- "could not request checkpoint because bgwriter not running");
- break;
- }
- }
- else if (kill(BgWriterShmem->bgwriter_pid, SIGINT) != 0)
- {
- if (ntries >= 20) /* max wait 2.0 sec */
- {
- elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
- "could not signal for checkpoint: %m");
- break;
- }
- }
- else
- break; /* signal sent successfully */
-
- CHECK_FOR_INTERRUPTS();
- pg_usleep(100000L); /* wait 0.1 sec, then retry */
- }
-
- /*
- * If requested, wait for completion. We detect completion according to
- * the algorithm given above.
- */
- if (flags & CHECKPOINT_WAIT)
- {
- int new_started,
- new_failed;
-
- /* Wait for a new checkpoint to start. */
- for (;;)
- {
- SpinLockAcquire(&bgs->ckpt_lck);
- new_started = bgs->ckpt_started;
- SpinLockRelease(&bgs->ckpt_lck);
-
- if (new_started != old_started)
- break;
-
- CHECK_FOR_INTERRUPTS();
- pg_usleep(100000L);
- }
-
- /*
- * We are waiting for ckpt_done >= new_started, in a modulo sense.
- */
- for (;;)
- {
- int new_done;
-
- SpinLockAcquire(&bgs->ckpt_lck);
- new_done = bgs->ckpt_done;
- new_failed = bgs->ckpt_failed;
- SpinLockRelease(&bgs->ckpt_lck);
-
- if (new_done - new_started >= 0)
- break;
-
- CHECK_FOR_INTERRUPTS();
- pg_usleep(100000L);
- }
-
- if (new_failed != old_failed)
- ereport(ERROR,
- (errmsg("checkpoint request failed"),
- errhint("Consult recent messages in the server log for details.")));
- }
-}
-
-/*
- * ForwardFsyncRequest
- * Forward a file-fsync request from a backend to the bgwriter
- *
- * Whenever a backend is compelled to write directly to a relation
- * (which should be seldom, if the bgwriter is getting its job done),
- * the backend calls this routine to pass over knowledge that the relation
- * is dirty and must be fsync'd before next checkpoint. We also use this
- * opportunity to count such writes for statistical purposes.
- *
- * segno specifies which segment (not block!) of the relation needs to be
- * fsync'd. (Since the valid range is much less than BlockNumber, we can
- * use high values for special flags; that's all internal to md.c, which
- * see for details.)
- *
- * To avoid holding the lock for longer than necessary, we normally write
- * to the requests[] queue without checking for duplicates. The bgwriter
- * will have to eliminate dups internally anyway. However, if we discover
- * that the queue is full, we make a pass over the entire queue to compact
- * it. This is somewhat expensive, but the alternative is for the backend
- * to perform its own fsync, which is far more expensive in practice. It
- * is theoretically possible a backend fsync might still be necessary, if
- * the queue is full and contains no duplicate entries. In that case, we
- * let the backend know by returning false.
- */
-bool
-ForwardFsyncRequest(RelFileNodeBackend rnode, ForkNumber forknum,
- BlockNumber segno)
-{
- BgWriterRequest *request;
-
- if (!IsUnderPostmaster)
- return false; /* probably shouldn't even get here */
-
- if (am_bg_writer)
- elog(ERROR, "ForwardFsyncRequest must not be called in bgwriter");
-
- LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE);
-
- /* Count all backend writes regardless of if they fit in the queue */
- BgWriterShmem->num_backend_writes++;
-
- /*
- * If the background writer isn't running or the request queue is full,
- * the backend will have to perform its own fsync request. But before
- * forcing that to happen, we can try to compact the background writer
- * request queue.
- */
- if (BgWriterShmem->bgwriter_pid == 0 ||
- (BgWriterShmem->num_requests >= BgWriterShmem->max_requests
- && !CompactBgwriterRequestQueue()))
- {
- /*
- * Count the subset of writes where backends have to do their own
- * fsync
- */
- BgWriterShmem->num_backend_fsync++;
- LWLockRelease(BgWriterCommLock);
- return false;
- }
- request = &BgWriterShmem->requests[BgWriterShmem->num_requests++];
- request->rnode = rnode;
- request->forknum = forknum;
- request->segno = segno;
- LWLockRelease(BgWriterCommLock);
- return true;
-}
-
-/*
- * CompactBgwriterRequestQueue
- * Remove duplicates from the request queue to avoid backend fsyncs.
- *
- * Although a full fsync request queue is not common, it can lead to severe
- * performance problems when it does happen. So far, this situation has
- * only been observed to occur when the system is under heavy write load,
- * and especially during the "sync" phase of a checkpoint. Without this
- * logic, each backend begins doing an fsync for every block written, which
- * gets very expensive and can slow down the whole system.
- *
- * Trying to do this every time the queue is full could lose if there
- * aren't any removable entries. But should be vanishingly rare in
- * practice: there's one queue entry per shared buffer.
- */
-static bool
-CompactBgwriterRequestQueue()
-{
- struct BgWriterSlotMapping
- {
- BgWriterRequest request;
- int slot;
- };
-
- int n,
- preserve_count;
- int num_skipped = 0;
- HASHCTL ctl;
- HTAB *htab;
- bool *skip_slot;
-
- /* must hold BgWriterCommLock in exclusive mode */
- Assert(LWLockHeldByMe(BgWriterCommLock));
-
- /* Initialize temporary hash table */
- MemSet(&ctl, 0, sizeof(ctl));
- ctl.keysize = sizeof(BgWriterRequest);
- ctl.entrysize = sizeof(struct BgWriterSlotMapping);
- ctl.hash = tag_hash;
- htab = hash_create("CompactBgwriterRequestQueue",
- BgWriterShmem->num_requests,
- &ctl,
- HASH_ELEM | HASH_FUNCTION);
-
- /* Initialize skip_slot array */
- skip_slot = palloc0(sizeof(bool) * BgWriterShmem->num_requests);
-
- /*
- * The basic idea here is that a request can be skipped if it's followed
- * by a later, identical request. It might seem more sensible to work
- * backwards from the end of the queue and check whether a request is
- * *preceded* by an earlier, identical request, in the hopes of doing less
- * copying. But that might change the semantics, if there's an
- * intervening FORGET_RELATION_FSYNC or FORGET_DATABASE_FSYNC request, so
- * we do it this way. It would be possible to be even smarter if we made
- * the code below understand the specific semantics of such requests (it
- * could blow away preceding entries that would end up being canceled
- * anyhow), but it's not clear that the extra complexity would buy us
- * anything.
- */
- for (n = 0; n < BgWriterShmem->num_requests; ++n)
- {
- BgWriterRequest *request;
- struct BgWriterSlotMapping *slotmap;
- bool found;
-
- request = &BgWriterShmem->requests[n];
- slotmap = hash_search(htab, request, HASH_ENTER, &found);
- if (found)
- {
- skip_slot[slotmap->slot] = true;
- ++num_skipped;
- }
- slotmap->slot = n;
- }
-
- /* Done with the hash table. */
- hash_destroy(htab);
-
- /* If no duplicates, we're out of luck. */
- if (!num_skipped)
- {
- pfree(skip_slot);
- return false;
- }
-
- /* We found some duplicates; remove them. */
- for (n = 0, preserve_count = 0; n < BgWriterShmem->num_requests; ++n)
- {
- if (skip_slot[n])
- continue;
- BgWriterShmem->requests[preserve_count++] = BgWriterShmem->requests[n];
- }
- ereport(DEBUG1,
- (errmsg("compacted fsync request queue from %d entries to %d entries",
- BgWriterShmem->num_requests, preserve_count)));
- BgWriterShmem->num_requests = preserve_count;
-
- /* Cleanup. */
- pfree(skip_slot);
- return true;
-}
-
-/*
- * AbsorbFsyncRequests
- * Retrieve queued fsync requests and pass them to local smgr.
- *
- * This is exported because it must be called during CreateCheckPoint;
- * we have to be sure we have accepted all pending requests just before
- * we start fsync'ing. Since CreateCheckPoint sometimes runs in
- * non-bgwriter processes, do nothing if not bgwriter.
- */
-void
-AbsorbFsyncRequests(void)
-{
- BgWriterRequest *requests = NULL;
- BgWriterRequest *request;
- int n;
-
- if (!am_bg_writer)
- return;
-
- /*
- * We have to PANIC if we fail to absorb all the pending requests (eg,
- * because our hashtable runs out of memory). This is because the system
- * cannot run safely if we are unable to fsync what we have been told to
- * fsync. Fortunately, the hashtable is so small that the problem is
- * quite unlikely to arise in practice.
- */
- START_CRIT_SECTION();
-
- /*
- * We try to avoid holding the lock for a long time by copying the request
- * array.
- */
- LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE);
-
- /* Transfer write count into pending pgstats message */
- BgWriterStats.m_buf_written_backend += BgWriterShmem->num_backend_writes;
- BgWriterStats.m_buf_fsync_backend += BgWriterShmem->num_backend_fsync;
-
- BgWriterShmem->num_backend_writes = 0;
- BgWriterShmem->num_backend_fsync = 0;
-
- n = BgWriterShmem->num_requests;
- if (n > 0)
- {
- requests = (BgWriterRequest *) palloc(n * sizeof(BgWriterRequest));
- memcpy(requests, BgWriterShmem->requests, n * sizeof(BgWriterRequest));
- }
- BgWriterShmem->num_requests = 0;
-
- LWLockRelease(BgWriterCommLock);
-
- for (request = requests; n > 0; request++, n--)
- RememberFsyncRequest(request->rnode, request->forknum, request->segno);
-
- if (requests)
- pfree(requests);
-
- END_CRIT_SECTION();
-}
/* PIDs of special child processes; 0 when not running */
static pid_t StartupPID = 0,
BgWriterPID = 0,
+ CheckpointerPID = 0,
WalWriterPID = 0,
WalReceiverPID = 0,
AutoVacPID = 0,
PM_WAIT_BACKUP, /* waiting for online backup mode to end */
PM_WAIT_READONLY, /* waiting for read only backends to exit */
PM_WAIT_BACKENDS, /* waiting for live backends to exit */
- PM_SHUTDOWN, /* waiting for bgwriter to do shutdown ckpt */
+ PM_SHUTDOWN, /* waiting for checkpointer to do shutdown ckpt */
PM_SHUTDOWN_2, /* waiting for archiver and walsenders to
* finish */
PM_WAIT_DEAD_END, /* waiting for dead_end children to exit */
#define StartupDataBase() StartChildProcess(StartupProcess)
#define StartBackgroundWriter() StartChildProcess(BgWriterProcess)
+#define StartCheckpointer() StartChildProcess(CheckpointerProcess)
#define StartWalWriter() StartChildProcess(WalWriterProcess)
#define StartWalReceiver() StartChildProcess(WalReceiverProcess)
* 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, and
- * postmaster/syslogger.c.
+ * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/pgstat.c,
+ * postmaster/syslogger.c and postmaster/checkpointer.c
*/
pqinitmask();
PG_SETMASK(&BlockSig);
* state that prevents it, start one. It doesn't matter if this
* fails, we'll just try again later.
*/
- if (BgWriterPID == 0 &&
- (pmState == PM_RUN || pmState == PM_RECOVERY ||
- pmState == PM_HOT_STANDBY))
- BgWriterPID = StartBackgroundWriter();
+ if (pmState == PM_RUN || pmState == PM_RECOVERY ||
+ pmState == PM_HOT_STANDBY)
+ {
+ if (BgWriterPID == 0)
+ BgWriterPID = StartBackgroundWriter();
+ if (CheckpointerPID == 0)
+ CheckpointerPID = StartCheckpointer();
+ }
/*
* Likewise, if we have lost the walwriter process, try to start a new
signal_child(StartupPID, SIGHUP);
if (BgWriterPID != 0)
signal_child(BgWriterPID, SIGHUP);
+ if (CheckpointerPID != 0)
+ signal_child(CheckpointerPID, SIGHUP);
if (WalWriterPID != 0)
signal_child(WalWriterPID, SIGHUP);
if (WalReceiverPID != 0)
/* and the walwriter too */
if (WalWriterPID != 0)
signal_child(WalWriterPID, SIGTERM);
+ if (BgWriterPID != 0)
+ signal_child(BgWriterPID, SIGTERM);
/*
* If we're in recovery, we can't kill the startup process
signal_child(StartupPID, SIGTERM);
if (WalReceiverPID != 0)
signal_child(WalReceiverPID, SIGTERM);
+ if (BgWriterPID != 0)
+ signal_child(BgWriterPID, SIGTERM);
if (pmState == PM_RECOVERY)
{
- /* only bgwriter is active in this state */
+ /* only checkpointer is active in this state */
pmState = PM_WAIT_BACKENDS;
}
else if (pmState == PM_RUN ||
signal_child(StartupPID, SIGQUIT);
if (BgWriterPID != 0)
signal_child(BgWriterPID, SIGQUIT);
+ if (CheckpointerPID != 0)
+ signal_child(CheckpointerPID, SIGQUIT);
if (WalWriterPID != 0)
signal_child(WalWriterPID, SIGQUIT);
if (WalReceiverPID != 0)
}
/*
- * Crank up the background writer, if we didn't do that already
+ * Crank up background tasks, if we didn't do that already
* when we entered consistent recovery state. It doesn't matter
* if this fails, we'll just try again later.
*/
if (BgWriterPID == 0)
BgWriterPID = StartBackgroundWriter();
+ if (CheckpointerPID == 0)
+ CheckpointerPID = StartCheckpointer();
/*
* Likewise, start other special children as needed. In a restart
if (pid == BgWriterPID)
{
BgWriterPID = 0;
+ if (!EXIT_STATUS_0(exitstatus))
+ HandleChildCrash(pid, exitstatus,
+ _("background writer process"));
+ continue;
+ }
+
+ /*
+ * Was it the checkpointer?
+ */
+ if (pid == CheckpointerPID)
+ {
+ CheckpointerPID = 0;
if (EXIT_STATUS_0(exitstatus) && pmState == PM_SHUTDOWN)
{
/*
- * OK, we saw normal exit of the bgwriter after it's been told
+ * OK, we saw normal exit of the checkpointer after it's been told
* to shut down. We expect that it wrote a shutdown
* checkpoint. (If for some reason it didn't, recovery will
* occur on next postmaster start.)
else
{
/*
- * Any unexpected exit of the bgwriter (including FATAL exit)
+ * Any unexpected exit of the checkpointer (including FATAL exit)
* is treated as a crash.
*/
HandleChildCrash(pid, exitstatus,
- _("background writer process"));
+ _("checkpointer process"));
}
continue;
}
/*
- * HandleChildCrash -- cleanup after failed backend, bgwriter, walwriter,
- * or autovacuum.
+ * HandleChildCrash -- cleanup after failed backend, bgwriter, checkpointer,
+ * walwriter or autovacuum.
*
* The objectives here are to clean up our local state about the child
* process, and to signal all other remaining children to quickdie.
signal_child(BgWriterPID, (SendStop ? SIGSTOP : SIGQUIT));
}
+ /* Take care of the checkpointer too */
+ if (pid == CheckpointerPID)
+ CheckpointerPID = 0;
+ else if (CheckpointerPID != 0 && !FatalError)
+ {
+ ereport(DEBUG2,
+ (errmsg_internal("sending %s to process %d",
+ (SendStop ? "SIGSTOP" : "SIGQUIT"),
+ (int) CheckpointerPID)));
+ signal_child(CheckpointerPID, (SendStop ? SIGSTOP : SIGQUIT));
+ }
+
/* Take care of the walwriter too */
if (pid == WalWriterPID)
WalWriterPID = 0;
{
/*
* PM_WAIT_BACKENDS state ends when we have no regular backends
- * (including autovac workers) and no walwriter or autovac launcher.
- * If we are doing crash recovery then we expect the bgwriter to exit
- * too, otherwise not. The archiver, stats, and syslogger processes
+ * (including autovac workers) and no walwriter, autovac launcher
+ * or bgwriter. If we are doing crash recovery then we expect the
+ * checkpointer to exit as well, otherwise not.
+ * The archiver, stats, and syslogger processes
* are disregarded since they are not connected to shared memory; we
* also disregard dead_end children here. Walsenders are also
* disregarded, they will be terminated later after writing the
if (CountChildren(BACKEND_TYPE_NORMAL | BACKEND_TYPE_AUTOVAC) == 0 &&
StartupPID == 0 &&
WalReceiverPID == 0 &&
- (BgWriterPID == 0 || !FatalError) &&
+ BgWriterPID == 0 &&
+ (CheckpointerPID == 0 || !FatalError) &&
WalWriterPID == 0 &&
AutoVacPID == 0)
{
/*
* If we get here, we are proceeding with normal shutdown. All
* the regular children are gone, and it's time to tell the
- * bgwriter to do a shutdown checkpoint.
+ * checkpointer to do a shutdown checkpoint.
*/
Assert(Shutdown > NoShutdown);
- /* Start the bgwriter if not running */
- if (BgWriterPID == 0)
- BgWriterPID = StartBackgroundWriter();
+ /* Start the checkpointer if not running */
+ if (CheckpointerPID == 0)
+ CheckpointerPID = StartCheckpointer();
/* And tell it to shut down */
- if (BgWriterPID != 0)
+ if (CheckpointerPID != 0)
{
- signal_child(BgWriterPID, SIGUSR2);
+ signal_child(CheckpointerPID, SIGUSR2);
pmState = PM_SHUTDOWN;
}
else
{
/*
- * If we failed to fork a bgwriter, just shut down. Any
+ * If we failed to fork a checkpointer, just shut down. Any
* required cleanup will happen at next restart. We set
* FatalError so that an "abnormal shutdown" message gets
* logged when we exit.
Assert(StartupPID == 0);
Assert(WalReceiverPID == 0);
Assert(BgWriterPID == 0);
+ Assert(CheckpointerPID == 0);
Assert(WalWriterPID == 0);
Assert(AutoVacPID == 0);
/* syslogger is not considered here */
*/
Assert(BgWriterPID == 0);
BgWriterPID = StartBackgroundWriter();
+ Assert(CheckpointerPID == 0);
+ CheckpointerPID = StartCheckpointer();
pmState = PM_RECOVERY;
}
ereport(LOG,
(errmsg("could not fork background writer process: %m")));
break;
+ case CheckpointerProcess:
+ ereport(LOG,
+ (errmsg("could not fork checkpointer process: %m")));
+ break;
case WalWriterProcess:
ereport(LOG,
(errmsg("could not fork WAL writer process: %m")));
projects / users / rhaas / postgres.git / commitdiff