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Commit21eb6ae

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Shave a few cycles in compare_pathkeys() by checking for pointer-identical
input lists before we grovel through the lists. This doesn't save much,but testing shows that the case of both inputs NIL is common enough thatit saves something. And this is used enough to be a hotspot.
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‎src/backend/optimizer/path/pathkeys.c

Lines changed: 12 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.96 2009/01/01 17:23:44 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.97 2009/02/28 03:51:05 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -332,6 +332,14 @@ compare_pathkeys(List *keys1, List *keys2)
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ListCell*key1,
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*key2;
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/*
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* Fall out quickly if we are passed two identical lists. This mostly
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* catches the case where both are NIL, but that's common enough to
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* warrant the test.
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*/
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if (keys1==keys2)
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returnPATHKEYS_EQUAL;
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forboth(key1,keys1,key2,keys2)
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{
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PathKey*pathkey1= (PathKey*)lfirst(key1);
@@ -354,11 +362,11 @@ compare_pathkeys(List *keys1, List *keys2)
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* If we reached the end of only one list, the other is longer and
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* therefore not a subset.
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*/
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if (key1==NULL&&key2==NULL)
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returnPATHKEYS_EQUAL;
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if (key1!=NULL)
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returnPATHKEYS_BETTER1;/* key1 is longer */
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returnPATHKEYS_BETTER2;/* key2 is longer */
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if (key2!=NULL)
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returnPATHKEYS_BETTER2;/* key2 is longer */
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returnPATHKEYS_EQUAL;
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}
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/*

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