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Commit25e46a5

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Fix a couple of oversights associated with the "physical tlist" optimization:
we had several code paths where a physical tlist could be used for the inputto a Sort node, which is a dumb idea because any unneeded table columns willincrease the volume of data the sort has to push around.(Unfortunately the easy-looking fix of calling disuse_physical_tlist duringmake_sort_xxx doesn't work because in most cases we're already committed tothe current input tlist --- it's been marked with sort column numbers, orwe've built grouping column numbers using it, etc. The tlist has to beselected properly at the calling level before we start constructing sort-colinformation. This is easy enough to do, we were just failing to take thepoint into consideration.)Back-patch to 8.3. I believe the problem probably exists clear back to 7.4when the physical tlist optimization was added, but I'm afraid to back-patchfurther than 8.3 without a great deal more study than I want to put into it.The code in this area has drifted a lot over time. The real-world importanceof these code paths is uncertain anyway --- I think in many cases we'dprobably prefer hash-based methods.
1 parentc5c7ba1 commit25e46a5

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3 files changed

+27
-12
lines changed

3 files changed

+27
-12
lines changed

‎src/backend/optimizer/plan/createplan.c‎

Lines changed: 9 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
*
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.239 2008/04/13 20:51:20 tgl Exp $
13+
* $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.240 2008/04/17 21:22:14 tgl Exp $
1414
*
1515
*-------------------------------------------------------------------------
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*/
@@ -115,6 +115,7 @@ static MergeJoin *make_mergejoin(List *tlist,
115115
staticSort*make_sort(PlannerInfo*root,Plan*lefttree,intnumCols,
116116
AttrNumber*sortColIdx,Oid*sortOperators,bool*nullsFirst,
117117
doublelimit_tuples);
118+
staticMaterial*make_material(Plan*lefttree);
118119

119120

120121
/*
@@ -616,12 +617,14 @@ create_unique_plan(PlannerInfo *root, UniquePath *best_path)
616617
* add any such expressions to the subplan's tlist.
617618
*
618619
* The subplan may have a "physical" tlist if it is a simple scan plan.
619-
* This should be left as-is if we don't need to add any expressions;
620+
* If we're going to sort, this should be reduced to the regular tlist,
621+
* so that we don't sort more data than we need to. For hashing, the
622+
* tlist should be left as-is if we don't need to add any expressions;
620623
* but if we do have to add expressions, then a projection step will be
621-
* needed at runtime anyway,andso we may as well remove unneeded items.
624+
* needed at runtime anyway, so we may as well remove unneeded items.
622625
* Therefore newtlist starts from build_relation_tlist() not just a
623626
* copy of the subplan's tlist; and we don't install it into the subplan
624-
* unless stuff has to be added.
627+
* unlesswe are sorting orstuff has to be added.
625628
*
626629
* To find the correct list of values to unique-ify, we look in the
627630
* information saved for IN expressions. If this code is ever used in
@@ -669,7 +672,7 @@ create_unique_plan(PlannerInfo *root, UniquePath *best_path)
669672
}
670673
}
671674

672-
if (newitems)
675+
if (newitems||best_path->umethod==UNIQUE_PATH_SORT)
673676
{
674677
/*
675678
* If the top plan node can't do projections, we need to add a Result
@@ -2850,7 +2853,7 @@ make_sort_from_groupcols(PlannerInfo *root,
28502853
sortColIdx,sortOperators,nullsFirst,-1.0);
28512854
}
28522855

2853-
Material*
2856+
staticMaterial*
28542857
make_material(Plan*lefttree)
28552858
{
28562859
Material*node=makeNode(Material);

‎src/backend/optimizer/plan/planner.c‎

Lines changed: 17 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.231 2008/04/01 00:48:33 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.232 2008/04/17 21:22:14 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -957,9 +957,23 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
957957
* Normal case --- create a plan according to query_planner's
958958
* results.
959959
*/
960+
boolneed_sort_for_grouping= false;
961+
960962
result_plan=create_plan(root,best_path);
961963
current_pathkeys=best_path->pathkeys;
962964

965+
/* Detect if we'll need an explicit sort for grouping */
966+
if (parse->groupClause&& !use_hashed_grouping&&
967+
!pathkeys_contained_in(group_pathkeys,current_pathkeys))
968+
{
969+
need_sort_for_grouping= true;
970+
/*
971+
* Always override query_planner's tlist, so that we don't
972+
* sort useless data from a "physical" tlist.
973+
*/
974+
need_tlist_eval= true;
975+
}
976+
963977
/*
964978
* create_plan() returns a plan with just a "flat" tlist of
965979
* required Vars. Usually we need to insert the sub_tlist as the
@@ -1054,8 +1068,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
10541068

10551069
if (parse->groupClause)
10561070
{
1057-
if (!pathkeys_contained_in(group_pathkeys,
1058-
current_pathkeys))
1071+
if (need_sort_for_grouping)
10591072
{
10601073
result_plan= (Plan*)
10611074
make_sort_from_groupcols(root,
@@ -1098,7 +1111,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
10981111
* Add an explicit sort if we couldn't make the path come out
10991112
* the way the GROUP node needs it.
11001113
*/
1101-
if (!pathkeys_contained_in(group_pathkeys,current_pathkeys))
1114+
if (need_sort_for_grouping)
11021115
{
11031116
result_plan= (Plan*)
11041117
make_sort_from_groupcols(root,

‎src/include/optimizer/planmain.h‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.106 2008/01/01 19:45:58 momjian Exp $
10+
* $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.107 2008/04/17 21:22:14 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -53,7 +53,6 @@ extern Group *make_group(PlannerInfo *root, List *tlist, List *qual,
5353
intnumGroupCols,AttrNumber*grpColIdx,Oid*grpOperators,
5454
doublenumGroups,
5555
Plan*lefttree);
56-
externMaterial*make_material(Plan*lefttree);
5756
externPlan*materialize_finished_plan(Plan*subplan);
5857
externUnique*make_unique(Plan*lefttree,List*distinctList);
5958
externLimit*make_limit(Plan*lefttree,Node*limitOffset,Node*limitCount,

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