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 f64553bbf878904bfcbde88eb85e4833690b661f..2477a17cfa3b4e4fca40b7a426212ce15523c94c 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 1.345 2008/11/15 19:43:46 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.346 2008/12/01 21:06:12 tgl Exp $
  *
  * NOTES
  *   Every node type that can appear in stored rules' parsetrees *must*
@@ -1563,6 +1563,7 @@ _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 e3e4e9f02c015e86cddd97fee08aa9580dfda9de..0ecdec10be2ac381692a0b0d70ebaad6f1d878bc 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 1.94 2008/10/04 21:56:53 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.95 2008/12/01 21:06:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -513,6 +513,12 @@ 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 c0351008750aab52e65f177b2f5623346cd30cca..3d35eb605d9d91967e32b0b50ce1789f1d236c2c 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 1.13 2008/10/21 20:42:52 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.14 2008/12/01 21:06:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1198,7 +1198,7 @@ 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
@@ -1220,7 +1220,7 @@ 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
@@ -1242,7 +1242,7 @@ 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 56074a469dc2eb3392c87b99fb1b89983cbe4c54..7b67d94700ef336b022ceaa7b9fade20936dcb3c 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 1.164 2008/11/11 18:13:32 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.165 2008/12/01 21:06:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -991,7 +991,8 @@ 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 */