Improve a few things in pg_walinspect

This improves a few things in pg_walinspect:
- Return NULL rather than empty strings in pg_get_wal_records_info() for
the block references and the record description if there is no
information provided by the fallback.  This point has been raised by
Peter Geoghegan.
- Add a check on XLogRecHasAnyBlockRefs() for pg_get_wal_block_info(),
to directly skip records that have no block references.  This speeds up
the function a bit, depending on the number of records that have no
block references.

Author: Bharath Rupireddy
Reviewed-by: Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACWL9RG8sGJHinggRNBTxgRWJTSxCkB+cE6=t3Phh=Ey+A@mail.gmail.com

diff --git a/contrib/pg_walinspect/pg_walinspect.c b/contrib/pg_walinspect/pg_walinspect.c
index 3b3215daf5a9afdb3f9259e8706bf1d6f881615e..5946b9e6e7121f30bd5c66ab415bd706a864cb8f 100644 (file)
--- a/contrib/pg_walinspect/pg_walinspect.c
+++ b/contrib/pg_walinspect/pg_walinspect.c
@@ -186,8 +186,6 @@ GetWALRecordInfo(XLogReaderState *record, Datum *values,
    RmgrData    desc;
    uint32      fpi_len = 0;
    StringInfoData rec_desc;
-   StringInfoData rec_blk_ref;
-   uint32      main_data_len;
    int         i = 0;
 
    desc = GetRmgr(XLogRecGetRmid(record));
@@ -199,12 +197,6 @@ GetWALRecordInfo(XLogReaderState *record, Datum *values,
    initStringInfo(&rec_desc);
    desc.rm_desc(&rec_desc, record);
 
-   /* Block references. */
-   initStringInfo(&rec_blk_ref);
-   XLogRecGetBlockRefInfo(record, false, true, &rec_blk_ref, &fpi_len);
-
-   main_data_len = XLogRecGetDataLen(record);
-
    values[i++] = LSNGetDatum(record->ReadRecPtr);
    values[i++] = LSNGetDatum(record->EndRecPtr);
    values[i++] = LSNGetDatum(XLogRecGetPrev(record));
@@ -212,10 +204,26 @@ GetWALRecordInfo(XLogReaderState *record, Datum *values,
    values[i++] = CStringGetTextDatum(desc.rm_name);
    values[i++] = CStringGetTextDatum(id);
    values[i++] = UInt32GetDatum(XLogRecGetTotalLen(record));
-   values[i++] = UInt32GetDatum(main_data_len);
+   values[i++] = UInt32GetDatum(XLogRecGetDataLen(record));
+
    values[i++] = UInt32GetDatum(fpi_len);
-   values[i++] = CStringGetTextDatum(rec_desc.data);
-   values[i++] = CStringGetTextDatum(rec_blk_ref.data);
+
+   if (rec_desc.len > 0)
+       values[i++] = CStringGetTextDatum(rec_desc.data);
+   else
+       nulls[i++] = true;
+
+   /* Block references. */
+   if (XLogRecHasAnyBlockRefs(record))
+   {
+       StringInfoData rec_blk_ref;
+
+       initStringInfo(&rec_blk_ref);
+       XLogRecGetBlockRefInfo(record, false, true, &rec_blk_ref, &fpi_len);
+       values[i++] = CStringGetTextDatum(rec_blk_ref.data);
+   }
+   else
+       nulls[i++] = true;
 
    Assert(i == ncols);
 }
@@ -377,6 +385,11 @@ pg_get_wal_block_info(PG_FUNCTION_ARGS)
    while (ReadNextXLogRecord(xlogreader) &&
           xlogreader->EndRecPtr <= end_lsn)
    {
+       CHECK_FOR_INTERRUPTS();
+
+       if (!XLogRecHasAnyBlockRefs(xlogreader))
+           continue;
+
        /* Use the tmp context so we can clean up after each tuple is done */
        old_cxt = MemoryContextSwitchTo(tmp_cxt);
 
@@ -385,8 +398,6 @@ pg_get_wal_block_info(PG_FUNCTION_ARGS)
        /* clean up and switch back */
        MemoryContextSwitchTo(old_cxt);
        MemoryContextReset(tmp_cxt);
-
-       CHECK_FOR_INTERRUPTS();
    }
 
    MemoryContextDelete(tmp_cxt);
@@ -483,8 +494,6 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 #define PG_GET_WAL_RECORDS_INFO_COLS 11
    XLogReaderState *xlogreader;
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-   Datum       values[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
-   bool        nulls[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
    MemoryContext old_cxt;
    MemoryContext tmp_cxt;
 
@@ -501,6 +510,9 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
    while (ReadNextXLogRecord(xlogreader) &&
           xlogreader->EndRecPtr <= end_lsn)
    {
+       Datum       values[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
+       bool        nulls[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
+
        /* Use the tmp context so we can clean up after each tuple is done */
        old_cxt = MemoryContextSwitchTo(tmp_cxt);