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heapam: Only set tuple's block once per page in pagemode

author Heikki Linnakangas <heikki.linnakangas@iki.fi>

Tue, 1 Apr 2025 10:24:27 +0000 (13:24 +0300)

committer Heikki Linnakangas <heikki.linnakangas@iki.fi>

Tue, 1 Apr 2025 10:24:27 +0000 (13:24 +0300)

Due to splitting the block id into two 16 bit integers, BlockIdSet()
is more expensive than one might think. Doing it once per returned
tuple shows up as a small but reliably reproducible cost. It's simple
enough to set the block number just once per block in pagemode, so do
so.

Author: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6@lzx3sjsqhmt6

src/backend/access/heap/heapam.c patch | blob | blame | history

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c

index 6e433db039ebb8b323a5cf7c25e67962a6c5f671..cedaa195cb6fa3f3465dc73a53c6321ec07686ea 100644 (file)

--- a/src/backend/access/heap/heapam.c

+++ b/src/backend/access/heap/heapam.c

@@ -1052,6 +1052,9 @@ heapgettup_pagemode(HeapScanDesc scan,

linesleft = scan->rs_ntuples;

lineindex = ScanDirectionIsForward(dir) ? 0 : linesleft - 1;

+ /* block is the same for all tuples, set it once outside the loop */

+ ItemPointerSetBlockNumber(&tuple->t_self, scan->rs_cblock);

/* lineindex now references the next or previous visible tid */

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