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Commit2904324

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heapam: Only set tuple's block once per page in pagemode
Due to splitting the block id into two 16 bit integers, BlockIdSet()is more expensive than one might think. Doing it once per returnedtuple shows up as a small but reliably reproducible cost. It's simpleenough to set the block number just once per block in pagemode, so doso.Author: Andres Freund <andres@anarazel.de>Discussion:https://www.postgresql.org/message-id/lxzj26ga6ippdeunz6kuncectr5gfuugmm2ry22qu6hcx6oid6@lzx3sjsqhmt6
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‎src/backend/access/heap/heapam.c

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1052,6 +1052,9 @@ heapgettup_pagemode(HeapScanDesc scan,
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linesleft=scan->rs_ntuples;
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lineindex=ScanDirectionIsForward(dir) ?0 :linesleft-1;
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1055+
/* block is the same for all tuples, set it once outside the loop */
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ItemPointerSetBlockNumber(&tuple->t_self,scan->rs_cblock);
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/* lineindex now references the next or previous visible tid */
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continue_page:
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@@ -1067,7 +1070,7 @@ heapgettup_pagemode(HeapScanDesc scan,
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tuple->t_data= (HeapTupleHeader)PageGetItem(page,lpp);
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tuple->t_len=ItemIdGetLength(lpp);
1070-
ItemPointerSet(&(tuple->t_self),scan->rs_cblock,lineoff);
1073+
ItemPointerSetOffsetNumber(&tuple->t_self,lineoff);
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/* skip any tuples that don't match the scan key */
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if (key!=NULL&&

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