Using canonicalize_qual() to get rid of duplicate index predicate

conditions is overkill; set_union() does the job about as well, and
much more efficiently.  Furthermore this avoids assuming that
canonicalize_qual() will check for duplicate clauses at all, which
it may not always do.

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 0a37df1..1c3bba0 100644 (file)
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.151 2003/12/28 21:57:37 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.152 2003/12/29 22:22:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3901,23 +3901,22 @@ genericcostestimate(Query *root, RelOptInfo *rel,
        /*
         * If the index is partial, AND the index predicate with the
         * explicitly given indexquals to produce a more accurate idea of the
-        * index restriction.  This may produce redundant clauses, which we
-        * hope that canonicalize_qual and clauselist_selectivity will deal with
-        * intelligently.
+        * index selectivity.  This may produce redundant clauses.  We can get
+        * rid of exact duplicates by using set_union().  We expect that most
+        * cases of partial redundancy (such as "x < 4" from the qual and
+        * "x < 5" from the predicate) will be recognized and handled correctly
+        * by clauselist_selectivity().  This assumption is somewhat fragile,
+        * since it depends on pred_test() and clauselist_selectivity() having
+        * similar capabilities, and there are certainly many cases where we will
+        * end up with a too-low selectivity estimate.  This will bias the system
+        * in favor of using partial indexes where possible, which is not
+        * necessarily a bad thing.  But it'd be nice to do better someday.
         *
-        * Note that index->indpred and indexQuals are both in implicit-AND form
-        * to start with, which we have to make explicit to hand to
-        * canonicalize_qual, and then we convert back to implicit-AND form.
+        * Note that index->indpred and indexQuals are both in implicit-AND form,
+        * so ANDing them together just takes merging the lists.
         */
        if (index->indpred != NIL)
-       {
-               Expr       *andedQuals;
-
-               andedQuals = make_ands_explicit(nconc(listCopy(index->indpred),
-                                                                                         indexQuals));
-               andedQuals = canonicalize_qual(andedQuals);
-               selectivityQuals = make_ands_implicit(andedQuals);
-       }
+               selectivityQuals = set_union(index->indpred, indexQuals);
 
        /* Estimate the fraction of main-table tuples that will be visited */
        *indexSelectivity = clauselist_selectivity(root, selectivityQuals,