From a1feb90ef32999f188f150795f896bd4ec839223 Mon Sep 17 00:00:00 2001 From: Tom Lane <tgl@sss.pgh.pa.us> Date: Mon, 1 Dec 2008 21:06:13 +0000 Subject: [PATCH] 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. --- src/backend/nodes/outfuncs.c | 3 ++- src/backend/optimizer/path/clausesel.c | 8 +++++++- src/backend/optimizer/path/equivclass.c | 8 ++++---- src/include/nodes/relation.h | 5 +++-- 4 files changed, 16 insertions(+), 8 deletions(-) diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c index f64553bbf87..2477a17cfa3 100644 --- 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 e3e4e9f02c0..0ecdec10be2 100644 --- 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 c0351008750..3d35eb605d9 100644 --- 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 56074a469dc..7b67d94700e 100644 --- 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 */ -- GitLab