From: Tom Lane Date: Mon, 20 Jun 2011 18:33:20 +0000 (-0400) Subject: Fix thinko in previous patch for optimizing EXISTS-within-EXISTS. X-Git-Tag: REL9_1_BETA3~56 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=6c560bef763f562a38fc629e54d0e20673efb9c1;p=postgresql Fix thinko in previous patch for optimizing EXISTS-within-EXISTS. When recursing after an optimization in pull_up_sublinks_qual_recurse, the available_rels value passed down must include only the relations that are in the righthand side of the new SEMI or ANTI join; it's incorrect to pull up a sub-select that refers to other relations, as seen in the added test case. Per report from BangarRaju Vadapalli. While at it, rethink the idea of recursing below a NOT EXISTS. That is essentially the same situation as pulling up ANY/EXISTS sub-selects that are in the ON clause of an outer join, and it has the same disadvantage: we'd force the two joins to be evaluated according to the syntactic nesting order, because the lower join will most likely not be able to commute with the ANTI join. That could result in having to form a rather large join product, whereas the handling of a correlated subselect is not quite that dumb. So until we can handle those cases better, #ifdef NOT_USED that case. (I think it's okay to pull up in the EXISTS/ANY cases, because SEMI joins aren't so inflexible about ordering.) Back-patch to 8.4, same as for previous patch in this area. Fortunately that patch hadn't made it into any shipped releases yet. --- diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c index 5d163292c5..ac622a34d9 100644 --- a/src/backend/optimizer/prep/prepjointree.c +++ b/src/backend/optimizer/prep/prepjointree.c @@ -246,6 +246,7 @@ pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode, * as a sublink that is executed only for row pairs that meet the * other join conditions. Fixing this seems to require considerable * restructuring of the executor, but maybe someday it can happen. + * (See also the comparable case in pull_up_sublinks_qual_recurse.) * * We don't expect to see any pre-existing JOIN_SEMI or JOIN_ANTI * nodes here. @@ -331,9 +332,7 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node, j->rarg = pull_up_sublinks_jointree_recurse(root, j->rarg, &child_rels); - /* Pulled-up ANY/EXISTS quals can use those rels too */ - child_rels = bms_add_members(child_rels, available_rels); - /* ... and any inserted joins get stacked onto j->rarg */ + /* Any inserted joins get stacked onto j->rarg */ j->quals = pull_up_sublinks_qual_recurse(root, j->quals, child_rels, @@ -355,9 +354,7 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node, j->rarg = pull_up_sublinks_jointree_recurse(root, j->rarg, &child_rels); - /* Pulled-up ANY/EXISTS quals can use those rels too */ - child_rels = bms_add_members(child_rels, available_rels); - /* ... and any inserted joins get stacked onto j->rarg */ + /* Any inserted joins get stacked onto j->rarg */ j->quals = pull_up_sublinks_qual_recurse(root, j->quals, child_rels, @@ -377,7 +374,6 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node, /* If the immediate argument of NOT is EXISTS, try to convert */ SubLink *sublink = (SubLink *) get_notclausearg((Expr *) node); JoinExpr *j; - Relids child_rels; if (sublink && IsA(sublink, SubLink)) { @@ -387,17 +383,27 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node, available_rels); if (j) { + /* + * For the moment, refrain from recursing underneath NOT. + * As in pull_up_sublinks_jointree_recurse, recursing here + * would result in inserting a join underneath an ANTI + * join with which it could not commute, and that could + * easily lead to a worse plan than what we've + * historically generated. + */ +#ifdef NOT_USED /* Yes; recursively process what we pulled up */ + Relids child_rels; + j->rarg = pull_up_sublinks_jointree_recurse(root, j->rarg, &child_rels); - /* Pulled-up ANY/EXISTS quals can use those rels too */ - child_rels = bms_add_members(child_rels, available_rels); - /* ... and any inserted joins get stacked onto j->rarg */ + /* Any inserted joins get stacked onto j->rarg */ j->quals = pull_up_sublinks_qual_recurse(root, j->quals, child_rels, &j->rarg); +#endif /* Now insert the new join node into the join tree */ j->larg = *jtlink; *jtlink = (Node *) j; diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out index 2440dcd822..8f180b9b19 100644 --- a/src/test/regress/expected/subselect.out +++ b/src/test/regress/expected/subselect.out @@ -530,3 +530,15 @@ select '1'::text in (select '1'::name union all select '1'::name); t (1 row) +-- +-- Test case for planner bug with nested EXISTS handling +-- +select a.thousand from tenk1 a, tenk1 b +where a.thousand = b.thousand + and exists ( select 1 from tenk1 c where b.hundred = c.hundred + and not exists ( select 1 from tenk1 d + where a.thousand = d.thousand ) ); + thousand +---------- +(0 rows) + diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql index 296e38b8c1..0d117c878f 100644 --- a/src/test/regress/sql/subselect.sql +++ b/src/test/regress/sql/subselect.sql @@ -341,3 +341,12 @@ from -- select '1'::text in (select '1'::name union all select '1'::name); + +-- +-- Test case for planner bug with nested EXISTS handling +-- +select a.thousand from tenk1 a, tenk1 b +where a.thousand = b.thousand + and exists ( select 1 from tenk1 c where b.hundred = c.hundred + and not exists ( select 1 from tenk1 d + where a.thousand = d.thousand ) );