Be a little smarter in group_clauses_by_indexkey_for_join: detect cases

where a joinclause is redundant with a restriction clause.  Original coding
believed this was impossible and didn't need to be checked for, but that
was a thinko ...

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 6e04c9c74aa5f5679d96caf567f3ac7a63b5d4b8..b9ccc770a431c923b1fe4e510bb7de9ebc1bc215 100644 (file)
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.149 2003/11/29 19:51:50 pgsql Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.150 2003/12/18 00:22:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -600,14 +600,43 @@ group_clauses_by_indexkey_for_join(Query *root,
    {
        Oid         curClass = classes[0];
        FastList    clausegroup;
+       int         numsources;
        List       *i;
 
        FastListInit(&clausegroup);
 
+       /*
+        * We can always use plain restriction clauses for the rel.  We scan
+        * these first because we want them first in the clausegroup list
+        * for the convenience of remove_redundant_join_clauses, which can
+        * never remove non-join clauses and hence won't be able to get rid
+        * of a non-join clause if it appears after a join clause it is
+        * redundant with.
+        */
+       foreach(i, rel->baserestrictinfo)
+       {
+           RestrictInfo *rinfo = (RestrictInfo *) lfirst(i);
+
+           /* Can't use pushed-down clauses in outer join */
+           if (isouterjoin && rinfo->ispusheddown)
+               continue;
+
+           if (match_clause_to_indexcol(rel,
+                                        index,
+                                        indexcol,
+                                        curClass,
+                                        rinfo->clause))
+               FastAppend(&clausegroup, rinfo);
+       }
+
+       /* found anything in base restrict list? */
+       numsources = (FastListValue(&clausegroup) != NIL) ? 1 : 0;
+
        /* Look for joinclauses that are usable with given outer_relids */
        foreach(i, rel->joininfo)
        {
            JoinInfo   *joininfo = (JoinInfo *) lfirst(i);
+           bool        jfoundhere = false;
            List       *j;
 
            if (!bms_is_subset(joininfo->unjoined_relids, outer_relids))
@@ -628,20 +657,21 @@ group_clauses_by_indexkey_for_join(Query *root,
                                                  rinfo->clause))
                {
                    FastAppend(&clausegroup, rinfo);
-                   jfound = true;
+                   if (!jfoundhere)
+                   {
+                       jfoundhere = true;
+                       jfound = true;
+                       numsources++;
+                   }
                }
            }
        }
 
        /*
-        * If we found join clauses in more than one joininfo list, we may
-        * now have clauses that are known redundant.  Get rid of 'em.
-        * (There is no point in looking at restriction clauses, because
-        * remove_redundant_join_clauses will never think they are
-        * redundant, so we do this before adding restriction clauses to
-        * the clause group.)
+        * If we found clauses in more than one list, we may now have clauses
+        * that are known redundant.  Get rid of 'em.
         */
-       if (FastListValue(&clausegroup) != NIL)
+       if (numsources > 1)
        {
            List       *nl;
 
@@ -651,23 +681,6 @@ group_clauses_by_indexkey_for_join(Query *root,
            FastListFromList(&clausegroup, nl);
        }
 
-       /* We can also use plain restriction clauses for the rel */
-       foreach(i, rel->baserestrictinfo)
-       {
-           RestrictInfo *rinfo = (RestrictInfo *) lfirst(i);
-
-           /* Can't use pushed-down clauses in outer join */
-           if (isouterjoin && rinfo->ispusheddown)
-               continue;
-
-           if (match_clause_to_indexcol(rel,
-                                        index,
-                                        indexcol,
-                                        curClass,
-                                        rinfo->clause))
-               FastAppend(&clausegroup, rinfo);
-       }
-
        /*
         * If no clauses match this key, we're done; we don't want to look
         * at keys to its right.