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Advance multiple array keys rightmost-first instead of leftmost-first

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during a bitmap index scan.  This cannot affect the query results
(since we're just dumping the TIDs into a bitmap) but it might offer
some advantage in locality of access to the index.  Per Greg Stark.
This commit is contained in:
Tom Lane 2008-03-18 03:54:52 +00:00
parent a2f1827dfd
commit 8e850b9159
1 changed files with 8 additions and 2 deletions
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10
src/backend/executor/nodeIndexscan.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.125 2008/01/01 19:45:49 momjian Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.126 2008/03/18 03:54:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -352,7 +352,13 @@ ExecIndexAdvanceArrayKeys(IndexArrayKeyInfo *arrayKeys, int numArrayKeys)
bool found = false;
int j;
for (j = 0; j < numArrayKeys; j++)
/*
* Note we advance the rightmost array key most quickly, since it will
* correspond to the lowest-order index column among the available
* qualifications. This is hypothesized to result in better locality
* of access in the index.
*/
for (j = numArrayKeys - 1; j >= 0; j--)
{
ScanKey scan_key = arrayKeys[j].scan_key;
int next_elem = arrayKeys[j].next_elem;