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help / color / mirror / Atom feedFrom: Melanie Plageman <melanieplageman@gmail.com>
Subject: [PATCH v11 04/17] BitmapPrefetch use prefetch block recheck for skip fetch
Date: Mon, 12 Feb 2024 19:03:24 -0500
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.g...
---
src/backend/executor/nodeBitmapHeapscan.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 83d9db8f39..5df3b5ca46 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -474,14 +474,9 @@ 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_NEED_TUPLE) &&
- (node->tbmres ? !node->tbmres->recheck : false) &&
+ !tbmpre->recheck &&
VM_ALL_VISIBLE(node->ss.ss_currentRelation,
tbmpre->blockno,
&node->pvmbuffer));
@@ -532,7 +527,7 @@ BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan)
/* As above, skip prefetch if we expect not to need page */
skip_fetch = (!(scan->rs_flags & SO_NEED_TUPLE) &&
- (node->tbmres ? !node->tbmres->recheck : false) &&
+ !tbmpre->recheck &&
VM_ALL_VISIBLE(node->ss.ss_currentRelation,
tbmpre->blockno,
&node->pvmbuffer));
--
2.40.1
--owzzsiozz6hgpp7e
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="v11-0005-Update-BitmapAdjustPrefetchIterator-parameter-ty.patch"
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To: pgsql-hackers@postgresql.org
Cc: melanieplageman@gmail.com
Subject: Re: [PATCH v11 04/17] BitmapPrefetch use prefetch block recheck for skip fetch
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