From 3df428a0428b821ed1c19bb19a18e0d3b3d60a4a Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Mon, 12 Feb 2024 19:03:24 -0500 Subject: [PATCH v5 04/14] BitmapPrefetch use prefetch block recheck for skip fetch As of 7c70996ebf0949b142a9, BitmapPrefetch() used the recheck flag for the current block to determine whether or not it could skip prefetching the proposed prefetch block. It makes more sense for it to use the recheck flag from the TBMIterateResult for the prefetch block instead. See this [1] thread on hackers reporting the issue. [1] https://www.postgresql.org/message-id/CAAKRu_bxrXeZ2rCnY8LyeC2Ls88KpjWrQ%2BopUrXDRXdcfwFZGA%40mail.gmail.com --- src/backend/executor/nodeBitmapHeapscan.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c index 2e4f87ea3a3..35ef26221ba 100644 --- a/src/backend/executor/nodeBitmapHeapscan.c +++ b/src/backend/executor/nodeBitmapHeapscan.c @@ -484,15 +484,9 @@ BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan) * skip this prefetch call, but continue to run the prefetch * logic normally. (Would it be better not to increment * prefetch_pages?) - * - * This depends on the assumption that the index AM will - * report the same recheck flag for this future heap page as - * it did for the current heap page; which is not a certainty - * but is true in many cases. */ - skip_fetch = (scan->rs_flags & SO_CAN_SKIP_FETCH && - (node->tbmres ? !node->tbmres->recheck : false) && + !tbmpre->recheck && VM_ALL_VISIBLE(node->ss.ss_currentRelation, tbmpre->blockno, &node->pvmbuffer)); @@ -543,7 +537,7 @@ BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan) /* As above, skip prefetch if we expect not to need page */ skip_fetch = (scan->rs_flags & SO_CAN_SKIP_FETCH && - (node->tbmres ? !node->tbmres->recheck : false) && + !tbmpre->recheck && VM_ALL_VISIBLE(node->ss.ss_currentRelation, tbmpre->blockno, &node->pvmbuffer)); -- 2.37.2