diff options
| author | Tom Lane | 2008-12-01 21:06:13 +0000 |
|---|---|---|
| committer | Tom Lane | 2008-12-01 21:06:13 +0000 |
| commit | a1feb90ef32999f188f150795f896bd4ec839223 (patch) | |
| tree | ef4ef4f938da0b0dced6f1e2b207f3e2ce7953f3 /src/include | |
| parent | 7fb27531e8f51448f061a007534db67e0467a23e (diff) | |
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.
Diffstat (limited to 'src/include')
| -rw-r--r-- | src/include/nodes/relation.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h index 56074a469d..7b67d94700 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 */ |