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Fix pull_up_sublinks' failure to handle nested pull-up opportunities.

Mon, 2 May 2011 19:56:43 +0000 (15:56 -0400)

After finding an EXISTS or ANY sub-select that can be converted to a
semi-join or anti-join, we should recurse into the body of the sub-select.
This allows cases such as EXISTS-within-EXISTS to be optimized properly.
The original coding would leave the lower sub-select as a SubLink, which
is no better and often worse than what we can do with a join. Per example
from Wayne Conrad.

Back-patch to 8.4. There is a related issue in older versions' handling
of pull_up_IN_clauses, but they're lame enough anyway about the whole area
that it seems not worth the extra work to try to fix.

src/backend/optimizer/plan/subselect.c patch | blob | blame | history

src/backend/optimizer/prep/prepjointree.c patch | blob | blame | history

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c

index cf503d51135d2b34947cf3eca30b8cb75be96859..30386a38091b92d04fe121cf7b650ae756492f3a 100644 (file)

--- a/src/backend/optimizer/plan/subselect.c

+++ b/src/backend/optimizer/plan/subselect.c

@@ -995,6 +995,11 @@ SS_process_ctes(PlannerInfo *root)

* (Notionally, we replace the SubLink with a constant TRUE, then elide the

* redundant constant from the qual.)

+ * On success, the caller is also responsible for recursively applying

+ * pull_up_sublinks processing to the rarg and quals of the returned JoinExpr.

+ * (On failure, there is no need to do anything, since pull_up_sublinks will

+ * be applied when we recursively plan the sub-select.)

+ *

* Side effects of a successful conversion include adding the SubLink's

* subselect to the query's rangetable, so that it can be referenced in

* the JoinExpr's rarg.

diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c

index 5a49768c6ce02d56d637de1c3f9c95d0db824bf7..93e9a94778760038b94a2e8eb455016e5d857933 100644 (file)

--- a/src/backend/optimizer/prep/prepjointree.c

+++ b/src/backend/optimizer/prep/prepjointree.c

@@ -317,6 +317,7 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,

{

SubLink *sublink = (SubLink *) node;

JoinExpr *j;

+ Relids child_rels;

/* Is it a convertible ANY or EXISTS clause? */

if (sublink->subLinkType == ANY_SUBLINK)

@@ -325,7 +326,18 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,

available_rels);

if (j)

{

- /* Yes, insert the new join node into the join tree */

+ /* Yes; recursively process what we pulled up */

+ 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 */

+ j->quals = pull_up_sublinks_qual_recurse(root,

+ j->quals,

+ child_rels,

+ &j->rarg);

+ /* Now insert the new join node into the join tree */

j->larg = *jtlink;

*jtlink = (Node *) j;

/* and return NULL representing constant TRUE */

@@ -338,7 +350,18 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,

available_rels);

if (j)

{

- /* Yes, insert the new join node into the join tree */

+ /* Yes; recursively process what we pulled up */

+ 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 */

+ j->quals = pull_up_sublinks_qual_recurse(root,

+ j->quals,

+ child_rels,

+ &j->rarg);

+ /* Now insert the new join node into the join tree */

j->larg = *jtlink;

*jtlink = (Node *) j;

/* and return NULL representing constant TRUE */

@@ -353,6 +376,7 @@ 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))

{

@@ -362,7 +386,18 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,

available_rels);

if (j)

{

- /* Yes, insert the new join node into the join tree */

+ /* Yes; recursively process what we pulled up */

+ 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 */

+ j->quals = pull_up_sublinks_qual_recurse(root,

+ j->quals,

+ child_rels,

+ &j->rarg);

+ /* Now insert the new join node into the join tree */

j->larg = *jtlink;

*jtlink = (Node *) j;

/* and return NULL representing constant TRUE */

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