Обсуждение: pgsql: Fix an oversight in the code that makes transitive-equality
pgsql: Fix an oversight in the code that makes transitive-equality
От
tgl@postgresql.org (Tom Lane)
Дата:
Log Message: ----------- 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. Tags: ---- REL8_2_STABLE Modified Files: -------------- pgsql/src/backend/nodes: outfuncs.c (r1.285.2.4 -> r1.285.2.5) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/outfuncs.c?r1=1.285.2.4&r2=1.285.2.5) pgsql/src/backend/optimizer/path: clausesel.c (r1.82.2.1 -> r1.82.2.2) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/clausesel.c?r1=1.82.2.1&r2=1.82.2.2) pathkeys.c (r1.79.2.1 -> r1.79.2.2) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/pathkeys.c?r1=1.79.2.1&r2=1.79.2.2) pgsql/src/include/nodes: relation.h (r1.128.2.5 -> r1.128.2.6) (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/relation.h?r1=1.128.2.5&r2=1.128.2.6)