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Save prune cycles by consistently clearing prune hints on all-visible pages

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All-visible pages can't contain prunable tuples. We already clear the
prune hint (pd_prune_xid) during pruning of all-visible pages, but we
were not doing so in vacuum phase three, nor initializing it for
all-frozen pages created by COPY FREEZE, and we were not clearing it on
standbys.

Because page hints are not WAL-logged, pages on a standby carry stale
pd_prune_xid values. After promotion, that stale hint triggers
unnecessary on-access pruning.

Fix this by clearing the prune hint everywhere we currently mark a heap
page all-visible. Clearing it when setting PD_ALL_VISIBLE ensures no
extra overhead.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/flat/CAAKRu_b-BMOyu0X-0jc_8bWNSbQ5K6JTEueayEhcQuw-OkCSKg%40mail.gmail.com
This commit is contained in:
Melanie Plageman 2026-03-02 11:05:59 -05:00
parent 1887d822f1
commit 8b9d42bf6b
3 changed files with 11 additions and 0 deletions
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1
src/backend/access/heap/heapam.c
View file

@ -2578,6 +2578,7 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
else if (all_frozen_set)
{
PageSetAllVisible(page);
PageClearPrunable(page);
visibilitymap_set_vmbits(BufferGetBlockNumber(buffer),
vmbuffer,
VISIBILITYMAP_ALL_VISIBLE |

7
src/backend/access/heap/heapam_xlog.c
View file

@ -164,7 +164,10 @@ heap_xlog_prune_freeze(XLogReaderState *record)
* modification would fail to clear the visibility map bit.
*/
if (vmflags & VISIBILITYMAP_VALID_BITS)
{
PageSetAllVisible(page);
PageClearPrunable(page);
}
MarkBufferDirty(buffer);
@ -305,6 +308,7 @@ heap_xlog_visible(XLogReaderState *record)
page = BufferGetPage(buffer);
PageSetAllVisible(page);
PageClearPrunable(page);
if (XLogHintBitIsNeeded())
PageSetLSN(page, lsn);
@ -734,7 +738,10 @@ heap_xlog_multi_insert(XLogReaderState *record)
/* XLH_INSERT_ALL_FROZEN_SET implies that all tuples are visible */
if (xlrec->flags & XLH_INSERT_ALL_FROZEN_SET)
{
PageSetAllVisible(page);
PageClearPrunable(page);
}
MarkBufferDirty(buffer);
}

3
src/backend/access/heap/vacuumlazy.c
View file

@ -1933,6 +1933,7 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno,
log_newpage_buffer(buf, true);
PageSetAllVisible(page);
PageClearPrunable(page);
visibilitymap_set(vacrel->rel, blkno, buf,
InvalidXLogRecPtr,
vmbuffer, InvalidTransactionId,
@ -2209,6 +2210,7 @@ lazy_scan_prune(LVRelState *vacrel,
* the VM bits clear, so there is no point in optimizing it.
*/
PageSetAllVisible(page);
PageClearPrunable(page);
MarkBufferDirty(buf);
/*
@ -2944,6 +2946,7 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
* set PD_ALL_VISIBLE.
*/
PageSetAllVisible(page);
PageClearPrunable(page);
visibilitymap_set_vmbits(blkno,
vmbuffer, vmflags,
vacrel->rel->rd_locator);