|
15 | 15 | * |
16 | 16 | * |
17 | 17 | * IDENTIFICATION |
18 | | - * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.151 2003/12/28 21:57:37 tgl Exp $ |
| 18 | + * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.152 2003/12/29 22:22:45 tgl Exp $ |
19 | 19 | * |
20 | 20 | *------------------------------------------------------------------------- |
21 | 21 | */ |
@@ -3901,23 +3901,22 @@ genericcostestimate(Query *root, RelOptInfo *rel, |
3901 | 3901 | /* |
3902 | 3902 | * If the index is partial, AND the index predicate with the |
3903 | 3903 | * explicitly given indexquals to produce a more accurate idea of the |
3904 | | - * index restriction. This may produce redundant clauses, which we |
3905 | | - * hope that canonicalize_qual and clauselist_selectivity will deal with |
3906 | | - * intelligently. |
| 3904 | + * index selectivity. This may produce redundant clauses. We can get |
| 3905 | + * rid of exact duplicates by using set_union(). We expect that most |
| 3906 | + * cases of partial redundancy (such as "x < 4" from the qual and |
| 3907 | + * "x < 5" from the predicate) will be recognized and handled correctly |
| 3908 | + * by clauselist_selectivity(). This assumption is somewhat fragile, |
| 3909 | + * since it depends on pred_test() and clauselist_selectivity() having |
| 3910 | + * similar capabilities, and there are certainly many cases where we will |
| 3911 | + * end up with a too-low selectivity estimate. This will bias the system |
| 3912 | + * in favor of using partial indexes where possible, which is not |
| 3913 | + * necessarily a bad thing. But it'd be nice to do better someday. |
3907 | 3914 | * |
3908 | | - * Note that index->indpred and indexQuals are both in implicit-AND form |
3909 | | - * to start with, which we have to make explicit to hand to |
3910 | | - * canonicalize_qual, and then we convert back to implicit-AND form. |
| 3915 | + * Note that index->indpred and indexQuals are both in implicit-AND form, |
| 3916 | + * so ANDing them together just takes merging the lists. |
3911 | 3917 | */ |
3912 | 3918 | if (index->indpred!=NIL) |
3913 | | -{ |
3914 | | -Expr*andedQuals; |
3915 | | - |
3916 | | -andedQuals=make_ands_explicit(nconc(listCopy(index->indpred), |
3917 | | -indexQuals)); |
3918 | | -andedQuals=canonicalize_qual(andedQuals); |
3919 | | -selectivityQuals=make_ands_implicit(andedQuals); |
3920 | | -} |
| 3919 | +selectivityQuals=set_union(index->indpred,indexQuals); |
3921 | 3920 |
|
3922 | 3921 | /* Estimate the fraction of main-table tuples that will be visited */ |
3923 | 3922 | *indexSelectivity=clauselist_selectivity(root,selectivityQuals, |
|