diff options
| -rw-r--r-- | src/backend/utils/sort/tuplesort.c | 26 |
1 files changed, 24 insertions, 2 deletions
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c index 636fdedcdb4..549ca8c484e 100644 --- a/src/backend/utils/sort/tuplesort.c +++ b/src/backend/utils/sort/tuplesort.c @@ -78,7 +78,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.41 2004/02/03 17:34:03 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.42 2004/03/17 22:24:58 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -2020,7 +2020,8 @@ comparetup_index(Tuplesortstate *state, const void *a, const void *b) { /* * This is almost the same as _bt_tuplecompare(), but we need to keep - * track of whether any null fields are present. + * track of whether any null fields are present. Also see the special + * treatment for equal keys at the end. */ IndexTuple tuple1 = (IndexTuple) a; IndexTuple tuple2 = (IndexTuple) b; @@ -2081,6 +2082,27 @@ comparetup_index(Tuplesortstate *state, const void *a, const void *b) errmsg("could not create unique index"), errdetail("Table contains duplicated values."))); + /* + * If key values are equal, we sort on ItemPointer. This does not + * affect validity of the finished index, but it offers cheap insurance + * against performance problems with bad qsort implementations that have + * trouble with large numbers of equal keys. + */ + { + BlockNumber blk1 = ItemPointerGetBlockNumber(&tuple1->t_tid); + BlockNumber blk2 = ItemPointerGetBlockNumber(&tuple2->t_tid); + + if (blk1 != blk2) + return (blk1 < blk2) ? -1 : 1; + } + { + OffsetNumber pos1 = ItemPointerGetOffsetNumber(&tuple1->t_tid); + OffsetNumber pos2 = ItemPointerGetOffsetNumber(&tuple2->t_tid); + + if (pos1 != pos2) + return (pos1 < pos2) ? -1 : 1; + } + return 0; } |