Fix an oversight in the code that makes transitive-equality deductions from

outer join clauses.  Given, say,
	... from a left join b on a.a1 = b.b1 where a.a1 = 42;
we'll deduce a clause b.b1 = 42 and then mark the original join clause
redundant (we can't remove it completely for reasons I don't feel like
squeezing into this log entry).  However the original implementation of
that wasn't bulletproof, because clause_selectivity() wouldn't honor
this_selec if given nonzero varRelid --- which in practice meant that
it worked as desired *except* when considering index scan quals.  Which
resulted in bogus underestimation of the size of the indexscan result for
an inner indexscan in an outer join, and consequently a possibly bad
choice of indexscan vs. bitmap scan.  Fix by introducing an explicit test
into clause_selectivity().  Also, to make sure we don't trigger that test
in corner cases, change the convention to be that this_selec > 1, not
this_selec = 1, means it's been marked redundant.  Per trouble report from
Scara Maccai.

Back-patch to 8.2, where the problem was introduced.

diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index c54cbc9d024e29e71619a7148a92c2f5317dc54a..6bc2595eafcf354640ad22b3c56d4ec18c6610ab 100644 (file)
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.322 2008/01/09 08:46:44 neilc Exp $
+ *       $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.322.2.1 2008/12/01 21:06:20 tgl Exp $
  *
  * NOTES
  *       Every node type that can appear in stored rules' parsetrees *must*
@@ -1459,6 +1459,7 @@ _outRestrictInfo(StringInfo str, RestrictInfo *node)
        WRITE_BITMAPSET_FIELD(right_relids);
        WRITE_NODE_FIELD(orclause);
        /* don't write parent_ec, leads to infinite recursion in plan tree dump */
+       WRITE_FLOAT_FIELD(this_selec, "%.4f");
        WRITE_NODE_FIELD(mergeopfamilies);
        /* don't write left_ec, leads to infinite recursion in plan tree dump */
        /* don't write right_ec, leads to infinite recursion in plan tree dump */

diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index e358c6990e248e0c3d895c57baf40679b0c60e07..072e527085b69c239cbf4a840d0f70f6f0f4a40f 100644 (file)
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.90 2008/01/11 17:00:45 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.90.2.1 2008/12/01 21:06:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -453,6 +453,12 @@ clause_selectivity(PlannerInfo *root,
                                return (Selectivity) 1.0;
                }
 
+               /*
+                * If the clause is marked redundant, always return 1.0.
+                */
+               if (rinfo->this_selec > 1)
+                       return (Selectivity) 1.0;
+
                /*
                 * If possible, cache the result of the selectivity calculation for
                 * the clause.  We can cache if varRelid is zero or the clause

diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 0e36af637f495b8de4b88c99470de60d917931b2..13ed31a5c96e9d94daefd208b38309f799e6f0dd 100644 (file)
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.9.2.1 2008/03/31 16:59:33 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.9.2.2 2008/12/01 21:06:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1197,7 +1197,7 @@ reconsider_outer_join_clauses(PlannerInfo *root)
                                        list_delete_cell(root->left_join_clauses, cell, prev);
                                /* we throw it back anyway (see notes above) */
                                /* but the thrown-back clause has no extra selectivity */
-                               rinfo->this_selec = 1.0;
+                               rinfo->this_selec = 2.0;
                                distribute_restrictinfo_to_rels(root, rinfo);
                        }
                        else
@@ -1219,7 +1219,7 @@ reconsider_outer_join_clauses(PlannerInfo *root)
                                        list_delete_cell(root->right_join_clauses, cell, prev);
                                /* we throw it back anyway (see notes above) */
                                /* but the thrown-back clause has no extra selectivity */
-                               rinfo->this_selec = 1.0;
+                               rinfo->this_selec = 2.0;
                                distribute_restrictinfo_to_rels(root, rinfo);
                        }
                        else
@@ -1241,7 +1241,7 @@ reconsider_outer_join_clauses(PlannerInfo *root)
                                        list_delete_cell(root->full_join_clauses, cell, prev);
                                /* we throw it back anyway (see notes above) */
                                /* but the thrown-back clause has no extra selectivity */
-                               rinfo->this_selec = 1.0;
+                               rinfo->this_selec = 2.0;
                                distribute_restrictinfo_to_rels(root, rinfo);
                        }
                        else

diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 56ff0f3f2fae9a1ecff9df388707684a5b50079c..3d4b9ddcf8c92a9f6684998e24d862a4e15259a7 100644 (file)
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.154.2.2 2008/04/21 20:54:24 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.154.2.3 2008/12/01 21:06:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -972,7 +972,8 @@ typedef struct RestrictInfo
 
        /* cache space for cost and selectivity */
        QualCost        eval_cost;              /* eval cost of clause; -1 if not yet set */
-       Selectivity this_selec;         /* selectivity; -1 if not yet set */
+       Selectivity this_selec;         /* selectivity; -1 if not yet set; >1 means
+                                                                * a redundant clause */
 
        /* valid if clause is mergejoinable, else NIL */
        List       *mergeopfamilies;    /* opfamilies containing clause operator */