From a7095841a82576e6984b31ffd04ae851fec91993 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sun, 26 Jan 2025 15:18:46 -0500 Subject: [PATCH v8 04/10] heapam: Use exclusive lock on old page in CLUSTER To be able to guarantee that we can set the hint bit, acquire an exclusive lock on the old buffer. We need the hint bits to be set as otherwise reform_and_rewrite_tuple() -> rewrite_heap_tuple() -> heap_freeze_tuple() will get confused. It'd be better if we somehow could avoid setting hint bits on the old page. A commonreason to use VACUUM FULL are very bloated tables - rewriting most of the old table before during VACUUM FULL doesn't exactly help. Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/backend/access/heap/heapam_handler.c | 13 ++++++++++++- src/backend/access/heap/heapam_visibility.c | 7 +++++++ 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c index dd4fe6bf62f..0c684786382 100644 --- a/src/backend/access/heap/heapam_handler.c +++ b/src/backend/access/heap/heapam_handler.c @@ -837,7 +837,18 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap, tuple = ExecFetchSlotHeapTuple(slot, false, NULL); buf = hslot->buffer; - LockBuffer(buf, BUFFER_LOCK_SHARE); + /* + * To be able to guarantee that we can set the hint bit, acquire an + * exclusive lock on the old buffer. We need the hint bits to be set + * as otherwise reform_and_rewrite_tuple() -> rewrite_heap_tuple() -> + * heap_freeze_tuple() will get confused. + * + * It'd be better if we somehow could avoid setting hint bits on the + * old page. One reason to use VACUUM FULL are very bloated tables - + * rewriting most of the old table before during VACUUM FULL doesn't + * exactly help... + */ + LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE); switch (HeapTupleSatisfiesVacuum(tuple, OldestXmin, buf)) { diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c index bf899c2d2c6..debf5d56b95 100644 --- a/src/backend/access/heap/heapam_visibility.c +++ b/src/backend/access/heap/heapam_visibility.c @@ -141,6 +141,13 @@ void HeapTupleSetHintBits(HeapTupleHeader tuple, Buffer buffer, uint16 infomask, TransactionId xid) { + /* + * The uses from heapam.c rely on being able to perform the hint bit + * updates, which can only be guaranteed if we are holding an exclusive + * lock on the buffer - which all callers are doing. + */ + Assert(BufferIsLockedByMeInMode(buffer, BUFFER_LOCK_EXCLUSIVE)); + SetHintBits(tuple, buffer, infomask, xid); } -- 2.48.1.76.g4e746b1a31.dirty