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Commitfbac127

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During btree index build, sort equal-keyed tuples according to their
TID (heap position). This doesn't do anything to the validity of thefinished index, but by pretending to qsort() that there are no reallyequal keys in the sort, we can avoid performance problems with qsortimplementations that have trouble with large numbers of equal keys.Patch from Manfred Koizar.
1 parent55f7c33 commitfbac127

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‎src/backend/utils/sort/tuplesort.c

Lines changed: 24 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -78,7 +78,7 @@
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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/utils/sort/tuplesort.c,v 1.41 2004/02/03 17:34:03 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.42 2004/03/17 22:24:58 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -2020,7 +2020,8 @@ comparetup_index(Tuplesortstate *state, const void *a, const void *b)
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{
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/*
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* This is almost the same as _bt_tuplecompare(), but we need to keep
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* track of whether any null fields are present.
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* track of whether any null fields are present. Also see the special
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* treatment for equal keys at the end.
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*/
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IndexTupletuple1= (IndexTuple)a;
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IndexTupletuple2= (IndexTuple)b;
@@ -2081,6 +2082,27 @@ comparetup_index(Tuplesortstate *state, const void *a, const void *b)
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errmsg("could not create unique index"),
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errdetail("Table contains duplicated values.")));
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/*
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* If key values are equal, we sort on ItemPointer. This does not
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* affect validity of the finished index, but it offers cheap insurance
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* against performance problems with bad qsort implementations that have
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* trouble with large numbers of equal keys.
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*/
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{
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BlockNumberblk1=ItemPointerGetBlockNumber(&tuple1->t_tid);
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BlockNumberblk2=ItemPointerGetBlockNumber(&tuple2->t_tid);
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if (blk1!=blk2)
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return (blk1<blk2) ?-1 :1;
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}
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{
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OffsetNumberpos1=ItemPointerGetOffsetNumber(&tuple1->t_tid);
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OffsetNumberpos2=ItemPointerGetOffsetNumber(&tuple2->t_tid);
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if (pos1!=pos2)
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return (pos1<pos2) ?-1 :1;
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}
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return0;
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}
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