From 8b93cbf472c2d4e3182a41e362b242d0b4d1b57d Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Tue, 20 Jun 2023 11:08:54 +1200 Subject: [PATCH v3 2/3] Fix race in SSI interaction with bitmap heap scan. When performing a bitmap heap scan, we don't want to miss concurrent writes that occurred after we observed the heap's rs_nblocks, but before we took predicate locks on index pages. Therefore, we can't skip fetching any heap tuples that are referenced by the index, because we need to test them all with CheckForSerializableConflictOut(). The old optimization that would ignore any references to blocks >= rs_nblocks gets in the way of that requirement, because it means that concurrent writes in that window are ignored. Removing that optimization shouldn't affect correctness at any isolation level, because any new tuples shouldn't be visible to an MVCC snapshot. There also shouldn't be any error-causing references to heap blocks past the end, because we should have held at least an AccessShareLock on the table before the index scan. It can't get smaller while our transaction is running. Back-patch to all supported releases. In release 11, the removed code is in a different location due to the table AM refactoring in commit bfbcad47, but not fundamentally different. Reported-by: Artem Anisimov Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com> Discussion: https://postgr.es/m/17949-a0f17035294a55e2%40postgresql.org --- src/backend/access/heap/heapam_handler.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c index 0755be8390..b41de7e3e1 100644 --- a/src/backend/access/heap/heapam_handler.c +++ b/src/backend/access/heap/heapam_handler.c @@ -2128,15 +2128,6 @@ heapam_scan_bitmap_next_block(TableScanDesc scan, hscan->rs_cindex = 0; hscan->rs_ntuples = 0; - /* - * Ignore any claimed entries past what we think is the end of the - * relation. It may have been extended after the start of our scan (we - * only hold an AccessShareLock, and it could be inserts from this - * backend). - */ - if (block >= hscan->rs_nblocks) - return false; - /* * Acquire pin on the target heap page, trading in any pin we held before. */ -- 2.40.1