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

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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
This commit is contained in:
Heikki Linnakangas 2025-04-01 13:24:27 +03:00
parent af0c248557
commit 2904324a88
1 changed files with 4 additions and 1 deletions
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5
src/backend/access/heap/heapam.c
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@ -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 */
continue_page:
@ -1067,7 +1070,7 @@ continue_page:
tuple->t_data = (HeapTupleHeader) PageGetItem(page, lpp);
tuple->t_len = ItemIdGetLength(lpp);
ItemPointerSet(&(tuple->t_self), scan->rs_cblock, lineoff);
ItemPointerSetOffsetNumber(&tuple->t_self, lineoff);
/* skip any tuples that don't match the scan key */
if (key != NULL &&