Be a little smarter about qual handling for semi-joins: a qual that mentions

only the outer side can be pushed down rather than having to be evaluated
at the join.

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 1208262..d1b590d 100644 (file)
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.143 2008/10/21 20:42:53 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.144 2008/10/25 19:51:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,6 +48,7 @@ static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
 static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                                bool is_deduced,
                                                bool below_outer_join,
+                                               JoinType jointype,
                                                Relids qualscope,
                                                Relids ojscope,
                                                Relids outerjoin_nonnullable);
@@ -342,7 +343,7 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                                                                                                 below_outer_join);
                        else
                                distribute_qual_to_rels(root, qual,
-                                                                               false, below_outer_join,
+                                                                               false, below_outer_join, JOIN_INNER,
                                                                                *qualscope, NULL, NULL);
                }
        }
@@ -452,7 +453,7 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                                                                                                 below_outer_join);
                        else
                                distribute_qual_to_rels(root, qual,
-                                                                               false, below_outer_join,
+                                                                               false, below_outer_join, j->jointype,
                                                                                *qualscope,
                                                                                ojscope, nonnullable_rels);
                }
@@ -712,6 +713,7 @@ make_outerjoininfo(PlannerInfo *root,
  * 'is_deduced': TRUE if the qual came from implied-equality deduction
  * 'below_outer_join': TRUE if the qual is from a JOIN/ON that is below the
  *             nullable side of a higher-level outer join
+ * 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause)
  * 'qualscope': set of baserels the qual's syntactic scope covers
  * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
  *             needed to form this join
@@ -728,6 +730,7 @@ static void
 distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                                bool is_deduced,
                                                bool below_outer_join,
+                                               JoinType jointype,
                                                Relids qualscope,
                                                Relids ojscope,
                                                Relids outerjoin_nonnullable)
@@ -848,11 +851,16 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                maybe_equivalence = false;
                maybe_outer_join = false;
        }
-       else if (bms_overlap(relids, outerjoin_nonnullable))
+       else if (bms_overlap(relids, outerjoin_nonnullable) &&
+                        (jointype != JOIN_SEMI ||
+                         bms_nonempty_difference(relids, outerjoin_nonnullable)))
        {
                /*
                 * The qual is attached to an outer join and mentions (some of the)
-                * rels on the nonnullable side, so it's not degenerate.
+                * rels on the nonnullable side, so it's not degenerate.  (For a
+                * JOIN_SEMI qual, we consider it non-degenerate only if it mentions
+                * both sides of the join --- if it mentions only one side, it can
+                * be pushed down.)
                 *
                 * We can't use such a clause to deduce equivalence (the left and
                 * right sides might be unequal above the join because one of them has
@@ -1024,7 +1032,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                                                                                   restrictinfo);
                                return;
                        }
-                       if (bms_equal(outerjoin_nonnullable, qualscope))
+                       if (jointype == JOIN_FULL)
                        {
                                /* FULL JOIN (above tests cannot match in this case) */
                                root->full_join_clauses = lappend(root->full_join_clauses,
@@ -1077,9 +1085,8 @@ distribute_sublink_quals_to_rels(PlannerInfo *root,
                Node   *qual = (Node *) lfirst(l);
 
                distribute_qual_to_rels(root, qual,
-                                                               false, below_outer_join,
-                                                               qualscope, ojscope,
-                                                               fslink->lefthand);
+                                                               false, below_outer_join, fslink->jointype,
+                                                               qualscope, ojscope, fslink->lefthand);
        }
 
        /* Now we can add the SpecialJoinInfo to join_info_list */
@@ -1373,7 +1380,7 @@ process_implied_equality(PlannerInfo *root,
         * Push the new clause into all the appropriate restrictinfo lists.
         */
        distribute_qual_to_rels(root, (Node *) clause,
-                                                       true, below_outer_join,
+                                                       true, below_outer_join, JOIN_INNER,
                                                        qualscope, NULL, NULL);
 }