From 5b170ea2c43b4ab828e67afc0bc875b1d593ecd6 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Mon, 29 Jun 2026 18:24:01 -0400 Subject: [PATCH v1] Update FSM after updating VM on-access b46e1e54d078de allowed setting the VM while on-access pruning, but it neglected to update the freespace map. Once the page was all-visible, vacuum could skip it, leading to stale freespace map values and, effectively, bloat. Fix it by updating the FSM if we updated the VM. --- src/backend/access/heap/pruneheap.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c index fdddd23035b..bcffec3055e 100644 --- a/src/backend/access/heap/pruneheap.c +++ b/src/backend/access/heap/pruneheap.c @@ -27,6 +27,7 @@ #include "miscadmin.h" #include "pgstat.h" #include "storage/bufmgr.h" +#include "storage/freespace.h" #include "utils/rel.h" #include "utils/snapmgr.h" @@ -321,6 +322,9 @@ heap_page_prune_opt(Relation relation, Buffer buffer, Buffer *vmbuffer, if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree) { + bool record_free_space = false; + Size freespace = 0; + /* OK, try to get exclusive buffer lock */ if (!ConditionalLockBufferForCleanup(buffer)) return; @@ -376,16 +380,32 @@ heap_page_prune_opt(Relation relation, Buffer buffer, Buffer *vmbuffer, if (presult.ndeleted > presult.nnewlpdead) pgstat_update_heap_dead_tuples(relation, presult.ndeleted - presult.nnewlpdead); + + /* + * If this prune newly set the page all-visible, VACUUM may later + * skip the page and thus not update its free space map (FSM) + * entry. Keep the FSM from going stale by recording it now. We do + * not want to update the freespace map otherwise (to reserve + * freespace on this page for future updates). + */ + if (presult.newly_all_visible) + { + record_free_space = true; + freespace = PageGetHeapFreeSpace(page); + } } /* And release buffer lock */ LockBuffer(buffer, BUFFER_LOCK_UNLOCK); /* - * We avoid reuse of any free space created on the page by unrelated - * UPDATEs/INSERTs by opting to not update the FSM at this point. The - * free space should be reused by UPDATEs to *this* page. + * RecordPageWithFreeSpace() only dirties the FSM when the recorded + * free-space category actually changes. Note that vacuum will still + * do FreeSpaceMapVacuum() for ranges of pages that are skipped, so we + * don't have to worry about that here. */ + if (record_free_space) + RecordPageWithFreeSpace(relation, BufferGetBlockNumber(buffer), freespace); } } -- 2.43.0