From b68cb29c547de3c4acd10f31aad47b453d154666 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Fri, 8 Mar 2024 16:00:22 +0200 Subject: [PATCH v8 1/3] Set all_visible_according_to_vm correctly with DISABLE_PAGE_SKIPPING It's important for 'all_visible_according_to_vm' to correctly reflect whether the VM bit is set or not, even when we are not trusting the VM to skip pages, because contrary to what the comment said, lazy_scan_prune() relies on it. If it's incorrectly set to 'false', when the VM bit is in fact set, lazy_scan_prune() will try to set the VM bit again and dirty the page unnecessarily. As a result, if you used DISABLE_PAGE_SKIPPING, all heap pages were dirtied, even if there were no changes. We would also fail to clear any VM bits that were set incorrectly. This was broken in commit 980ae17310, so backpatch to v16. Backpatch-through: 16 Reviewed-by: Melanie Plageman Discussion: https://www.postgresql.org/message-id/3df2b582-dc1c-46b6-99b6-38eddd1b2784@iki.fi --- src/backend/access/heap/vacuumlazy.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index 8b320c3f89a..ac55ebd2ae5 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -1136,11 +1136,7 @@ lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, /* DISABLE_PAGE_SKIPPING makes all skipping unsafe */ if (!vacrel->skipwithvm) - { - /* Caller shouldn't rely on all_visible_according_to_vm */ - *next_unskippable_allvis = false; break; - } /* * Aggressive VACUUM caller can't skip pages just because they are -- 2.39.2