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Extend set-operation planning to keep track of the sort ordering induced

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by the set operation, so that redundant sorts at higher levels can be
avoided.  This was foreseen a good while back, but not done.  Per request
from Karel Zak.
This commit is contained in:
Tom Lane
2004-04-07 18:17:25 +00:00
parent 5d1af6aee3
commit 989067bd22
3 changed files with 63 additions and 29 deletions
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27
src/backend/optimizer/plan/planner.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.167 2004/02/13 22:26:30 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.168 2004/04/07 18:17:24 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -572,11 +572,23 @@ grouping_planner(Query *parse, double tuple_fraction)
if (parse->setOperations)
{
List *set_sortclauses;
/*
* Construct the plan for set operations. The result will not
* need any work except perhaps a top-level sort and/or LIMIT.
*/
result_plan = plan_set_operations(parse);
result_plan = plan_set_operations(parse,
&set_sortclauses);
/*
* Calculate pathkeys representing the sort order (if any) of the
* set operation's result. We have to do this before overwriting
* the sort key information...
*/
current_pathkeys = make_pathkeys_for_sortclauses(set_sortclauses,
result_plan->targetlist);
current_pathkeys = canonicalize_pathkeys(parse, current_pathkeys);
/*
* We should not need to call preprocess_targetlist, since we must
@ -599,16 +611,7 @@ grouping_planner(Query *parse, double tuple_fraction)
errmsg("SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT")));
/*
* We set current_pathkeys NIL indicating we do not know sort
* order. This is correct when the top set operation is UNION
* ALL, since the appended-together results are unsorted even if
* the subplans were sorted. For other set operations we could be
* smarter --- room for future improvement!
*/
current_pathkeys = NIL;
/*
* Calculate pathkeys that represent ordering requirements
* Calculate pathkeys that represent result ordering requirements
*/
sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
tlist);