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pg prewarm heap scan #790

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pg prewarm heap scan #790

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49f9413
c
HaoyuHuang Oct 28, 2025
e522e2d
c
HaoyuHuang Oct 28, 2025
95abdee
c
HaoyuHuang Oct 31, 2025
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33 changes: 32 additions & 1 deletion contrib/pg_prewarm/pg_prewarm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
#include <sys/stat.h>
#include <unistd.h>

#include "access/heapam.h"
#include "access/relation.h"
#include "fmgr.h"
#include "miscadmin.h"
Expand All @@ -35,7 +36,8 @@ typedef enum
{
PREWARM_PREFETCH,
PREWARM_READ,
PREWARM_BUFFER
PREWARM_BUFFER,
PREWARM_TUPLE,
} PrewarmType;

static PGIOAlignedBlock blockbuffer;
Expand Down Expand Up @@ -88,6 +90,8 @@ pg_prewarm(PG_FUNCTION_ARGS)
ptype = PREWARM_READ;
else if (strcmp(ttype, "buffer") == 0)
ptype = PREWARM_BUFFER;
else if (strcmp(ttype, "tuple") == 0)
ptype = PREWARM_TUPLE;
else
{
ereport(ERROR,
Expand Down Expand Up @@ -210,6 +214,33 @@ pg_prewarm(PG_FUNCTION_ARGS)
++blocks_done;
}
}
else if (ptype == PREWARM_TUPLE)
{
if (get_relkind_objtype(rel->rd_rel->relkind) == OBJECT_TABLE && forkNumber == MAIN_FORKNUM)
{
uint32 scan_flags = SO_TYPE_SEQSCAN | SO_TEMP_SNAPSHOT;
HeapTuple tuple;
Snapshot snapshot;
TableScanDesc scan;

elog(LOG, "pg_prewarm: SeqScan relation \"%s\" starting %ld for %ld blocks", RelationGetRelationName(rel), first_block, last_block - first_block + 1);
// Use heap scan to set hint bits on every tuple. SO_ALLOW_PAGEMODE is intentionally NOT SET.
// Otherwise, when a page is all visible, tuple hint bits won't be set.
snapshot = RegisterSnapshot(GetTransactionSnapshot());
scan = heap_beginscan(rel, snapshot, 0, NULL, NULL, scan_flags);
heap_setscanlimits(scan, first_block, last_block - first_block + 1);
while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
{
CHECK_FOR_INTERRUPTS();
}
heap_endscan(scan);
} else
{
ereport(INFO,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("tuple prewarm is only supported for heap relations on main fork")));
}
}

/* Close relation, release lock. */
relation_close(rel, AccessShareLock);
Expand Down