From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 2 Mar 2026 16:05:59 +0000 (-0500)
Subject: Save prune cycles by consistently clearing prune hints on all-visible pages
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8b9d42bf6bd29b855a6bee21aa6010c070980086;p=thirdparty%2Fpostgresql.git

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

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
---

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index d534258e547..a231563f0df 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -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 |
diff --git a/src/backend/access/heap/heapam_xlog.c b/src/backend/access/heap/heapam_xlog.c
index f765345e9e4..6d39a5fff7c 100644
--- a/src/backend/access/heap/heapam_xlog.c
+++ b/src/backend/access/heap/heapam_xlog.c
@@ -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);
 	}
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 5d271d80967..5b6f2441f6b 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -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);