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Teach the planner to remove SubqueryScan nodes from the plan if they

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aren't doing anything useful (ie, neither selection nor projection).
Also, extend to SubqueryScan the hacks already in place to avoid
unnecessary ExecProject calls when the result would just be the same
tuple the subquery already delivered.  This saves some overhead in
UNION and other set operations, as well as avoiding overhead for
unflatten-able subqueries.  Per example from Sokolov Yura.
This commit is contained in:
Tom Lane
2005-05-22 22:30:20 +00:00
parent c61207b091
commit e2159f3842
13 changed files with 605 additions and 177 deletions
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52
src/backend/optimizer/util/clauses.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.196 2005/04/23 04:42:53 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.197 2005/05/22 22:30:20 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@@ -3026,8 +3026,6 @@ query_tree_walker(Query *query,
void *context,
int flags)
{
ListCell *rt;
Assert(query != NULL && IsA(query, Query));
if (walker((Node *) query->targetList, context))
@@ -3044,7 +3042,25 @@ query_tree_walker(Query *query,
return true;
if (walker(query->in_info_list, context))
return true;
foreach(rt, query->rtable)
if (range_table_walker(query->rtable, walker, context, flags))
return true;
return false;
}
/*
* range_table_walker is just the part of query_tree_walker that scans
* a query's rangetable. This is split out since it can be useful on
* its own.
*/
bool
range_table_walker(List *rtable,
bool (*walker) (),
void *context,
int flags)
{
ListCell *rt;
foreach(rt, rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
@@ -3532,9 +3548,6 @@ query_tree_mutator(Query *query,
void *context,
int flags)
{
List *newrt;
ListCell *rt;
Assert(query != NULL && IsA(query, Query));
if (!(flags & QTW_DONT_COPY_QUERY))
@@ -3552,8 +3565,26 @@ query_tree_mutator(Query *query,
MUTATE(query->limitOffset, query->limitOffset, Node *);
MUTATE(query->limitCount, query->limitCount, Node *);
MUTATE(query->in_info_list, query->in_info_list, List *);
newrt = NIL;
foreach(rt, query->rtable)
query->rtable = range_table_mutator(query->rtable,
mutator, context, flags);
return query;
}
/*
* range_table_mutator is just the part of query_tree_mutator that processes
* a query's rangetable. This is split out since it can be useful on
* its own.
*/
List *
range_table_mutator(List *rtable,
Node *(*mutator) (),
void *context,
int flags)
{
List *newrt = NIL;
ListCell *rt;
foreach(rt, rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
RangeTblEntry *newrte;
@@ -3592,8 +3623,7 @@ query_tree_mutator(Query *query,
}
newrt = lappend(newrt, newrte);
}
query->rtable = newrt;
return query;
return newrt;
}
/*