Fix planner to do the right thing when a degenerate outer join (one whose

joinclause doesn't use any outer-side vars) requires a "bushy" plan to be
created.  The normal heuristic to avoid joins with no joinclause has to be
overridden in that case.  Problem is new in 8.2; before that we forced the
outer join order anyway.  Per example from Teodor.

diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c
index 240672e..197efac 100644 (file)
--- a/src/backend/optimizer/geqo/geqo_eval.c
+++ b/src/backend/optimizer/geqo/geqo_eval.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_eval.c,v 1.81 2006/10/24 17:50:22 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_eval.c,v 1.82 2006/12/12 21:31:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -258,7 +258,7 @@ desirable_join(PlannerInfo *root,
        /*
         * Join if there is an applicable join clause.
         */
-       if (have_relevant_joinclause(outer_rel, inner_rel))
+       if (have_relevant_joinclause(root, outer_rel, inner_rel))
                return true;
 
        /*

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 17b5f31..9801795 100644 (file)
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.81 2006/10/24 17:50:22 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.82 2006/12/12 21:31:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -147,8 +147,13 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels)
                        ListCell   *other_rels;
                        ListCell   *r2;
 
-                       if (old_rel->joininfo == NIL)
-                               continue;               /* we ignore clauseless joins here */
+                       /*
+                        * We can ignore clauseless joins here, *except* when there are
+                        * outer joins --- then we might have to force a bushy outer
+                        * join.  See have_relevant_joinclause().
+                        */
+                       if (old_rel->joininfo == NIL && root->oj_info_list == NIL)
+                               continue;
 
                        if (k == other_level)
                                other_rels = lnext(r);  /* only consider remaining rels */
@@ -166,7 +171,7 @@ make_rels_by_joins(PlannerInfo *root, int level, List **joinrels)
                                         * pair of rels.  Do so if there is at least one usable
                                         * join clause.
                                         */
-                                       if (have_relevant_joinclause(old_rel, new_rel))
+                                       if (have_relevant_joinclause(root, old_rel, new_rel))
                                        {
                                                RelOptInfo *jrel;
 
@@ -270,7 +275,7 @@ make_rels_by_clause_joins(PlannerInfo *root,
                RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
 
                if (!bms_overlap(old_rel->relids, other_rel->relids) &&
-                       have_relevant_joinclause(old_rel, other_rel))
+                       have_relevant_joinclause(root, old_rel, other_rel))
                {
                        RelOptInfo *jrel;
 

diff --git a/src/backend/optimizer/util/joininfo.c b/src/backend/optimizer/util/joininfo.c
index 9aab377..bd54a13 100644 (file)
--- a/src/backend/optimizer/util/joininfo.c
+++ b/src/backend/optimizer/util/joininfo.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/util/joininfo.c,v 1.44 2006/03/05 15:58:31 momjian Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/util/joininfo.c,v 1.45 2006/12/12 21:31:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,7 +24,8 @@
  *             the two given relations.
  */
 bool
-have_relevant_joinclause(RelOptInfo *rel1, RelOptInfo *rel2)
+have_relevant_joinclause(PlannerInfo *root,
+                                                RelOptInfo *rel1, RelOptInfo *rel2)
 {
        bool            result = false;
        Relids          join_relids;
@@ -53,6 +54,40 @@ have_relevant_joinclause(RelOptInfo *rel1, RelOptInfo *rel2)
                }
        }
 
+       /*
+        * It's possible that the rels correspond to the left and right sides
+        * of a degenerate outer join, that is, one with no joinclause mentioning
+        * the non-nullable side.  The above scan will then have failed to locate
+        * any joinclause indicating we should join, but nonetheless we must
+        * allow the join to occur.
+        *
+        * Note: we need no comparable check for IN-joins because we can handle
+        * sequential buildup of an IN-join to multiple outer-side rels; therefore
+        * the "last ditch" case in make_rels_by_joins() always succeeds.  We
+        * could dispense with this hack if we were willing to try bushy plans
+        * in the "last ditch" case, but that seems too expensive.
+        */
+       if (!result)
+       {
+               foreach(l, root->oj_info_list)
+               {
+                       OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
+
+                       /* ignore full joins --- other mechanisms handle them */
+                       if (ojinfo->is_full_join)
+                               continue;
+
+                       if ((bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
+                                bms_is_subset(ojinfo->min_righthand, rel2->relids)) ||
+                               (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
+                                bms_is_subset(ojinfo->min_righthand, rel1->relids)))
+                       {
+                               result = true;
+                               break;
+                       }
+               }
+       }
+
        bms_free(join_relids);
 
        return result;

diff --git a/src/include/optimizer/joininfo.h b/src/include/optimizer/joininfo.h
index 7c4909e..1480f77 100644 (file)
--- a/src/include/optimizer/joininfo.h
+++ b/src/include/optimizer/joininfo.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/joininfo.h,v 1.31 2006/03/05 15:58:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/joininfo.h,v 1.32 2006/12/12 21:31:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,7 +17,8 @@
 #include "nodes/relation.h"
 
 
-extern bool have_relevant_joinclause(RelOptInfo *rel1, RelOptInfo *rel2);
+extern bool have_relevant_joinclause(PlannerInfo *root,
+                                                                        RelOptInfo *rel1, RelOptInfo *rel2);
 
 extern void add_join_clause_to_rels(PlannerInfo *root,
                                                RestrictInfo *restrictinfo,