From 9ef95e019b09ea5f1bc62a88a2be4a0480197ada Mon Sep 17 00:00:00 2001 From: Masahiko Sawada Date: Wed, 21 May 2025 14:13:02 -0700 Subject: [PATCH v1] Fix assertion when decrementing eager_scan_remaining_successes counter. Previously, we asserted that the eager scan's success counter was positive before decrementing it. However, this assumption was incorrect, as it's possible that some blocks have already been eagerly scanned by the time eager scanning is disabled. This commit replaces the assertion with a guard to handle this scenario gracefully. With this change, we continue to allow read-ahead operations by the read stream that exceed the success and failure caps. While there is a possibility that overruns will trigger eager scans of additional pages (beyond 20% of the total number of all-visible but not all-frozen pages), this does not pose a practical concern as the overruns will not be huge and remain within acceptable range. Reviewed-by: Melanie Plageman Discussion: https://postgr.es/m/CAD21AoConf6tkVCv-=JhQJj56kYsDwo4jG5+WqgT+ukSkYomSQ@mail.gmail.com --- src/backend/access/heap/vacuumlazy.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index f28326bad09..0811a59b37a 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -1413,11 +1413,24 @@ lazy_scan_heap(LVRelState *vacrel) if (vm_page_frozen) { - Assert(vacrel->eager_scan_remaining_successes > 0); - vacrel->eager_scan_remaining_successes--; + if (vacrel->eager_scan_remaining_successes > 0) + vacrel->eager_scan_remaining_successes--; if (vacrel->eager_scan_remaining_successes == 0) { + /* + * Report only once that we disabled eager scanning. This + * check is required because we might have eagerly read + * more blocks and we could reach here even after + * disabling eager scanning. + */ + if (vacrel->eager_scan_max_fails_per_region > 0) + ereport(vacrel->verbose ? INFO : DEBUG2, + (errmsg("disabling eager scanning after freezing %u eagerly scanned blocks of \"%s.%s.%s\"", + orig_eager_scan_success_limit, + vacrel->dbname, vacrel->relnamespace, + vacrel->relname))); + /* * If we hit our success cap, permanently disable eager * scanning by setting the other eager scan management @@ -1426,12 +1439,6 @@ lazy_scan_heap(LVRelState *vacrel) vacrel->eager_scan_remaining_fails = 0; vacrel->next_eager_scan_region_start = InvalidBlockNumber; vacrel->eager_scan_max_fails_per_region = 0; - - ereport(vacrel->verbose ? INFO : DEBUG2, - (errmsg("disabling eager scanning after freezing %u eagerly scanned blocks of \"%s.%s.%s\"", - orig_eager_scan_success_limit, - vacrel->dbname, vacrel->relnamespace, - vacrel->relname))); } } else -- 2.43.5