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Teach planner how to propagate pathkeys from sub-SELECTs in FROM up to
the outer query. (The implementation is a bit klugy, but it would take nontrivial restructuring to make it nicer, which this is probably not worth.) This avoids unnecessary sort steps in examples like SELECT foo,count(*) FROM (SELECT ... ORDER BY foo,bar) sub GROUP BY foo which means there is now a reasonable technique for controlling the order of inputs to custom aggregates, even in the grouping case.
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9 files changed

+172
-29
lines changed

9 files changed

+172
-29
lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 6 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.96 2003/02/08 20:20:54 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.97 2003/02/15 20:12:40 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -291,6 +291,7 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
291291
Index rti, RangeTblEntry *rte)
292292
{
293293
Query *subquery = rte->subquery;
294+
List *pathkeys;
294295

295296
/*
296297
* If there are any restriction clauses that have been attached to the
@@ -351,8 +352,11 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
351352
/* Mark rel with estimated output rows, width, etc */
352353
set_baserel_size_estimates(root, rel);
353354

355+
/* Convert subquery pathkeys to outer representation */
356+
pathkeys = build_subquery_pathkeys(root, rel, subquery);
357+
354358
/* Generate appropriate path */
355-
add_path(rel, create_subqueryscan_path(rel));
359+
add_path(rel, create_subqueryscan_path(rel, pathkeys));
356360

357361
/* Select cheapest path (pretty easy in this case...) */
358362
set_cheapest(rel);

‎src/backend/optimizer/path/pathkeys.c

Lines changed: 138 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
* Portions Copyright (c) 1994, Regents of the University of California
1212
*
1313
* IDENTIFICATION
14-
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.46 2003/02/08 20:20:54 tgl Exp $
14+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/pathkeys.c,v 1.47 2003/02/15 20:12:40 tgl Exp $
1515
*
1616
*-------------------------------------------------------------------------
1717
*/
@@ -366,6 +366,31 @@ canonicalize_pathkeys(Query *root, List *pathkeys)
366366
return new_pathkeys;
367367
}
368368

369+
370+
/*
371+
* count_canonical_peers
372+
* Given a PathKeyItem, find the equi_key_list subset it is a member of,
373+
* if any. If so, return the number of other members of the set.
374+
* If not, return 0 (without actually adding it to our equi_key_list).
375+
*
376+
* This is a hack to support the rather bogus heuristics in
377+
* build_subquery_pathkeys.
378+
*/
379+
static int
380+
count_canonical_peers(Query *root, PathKeyItem *item)
381+
{
382+
List *cursetlink;
383+
384+
foreach(cursetlink, root->equi_key_list)
385+
{
386+
List *curset = lfirst(cursetlink);
387+
388+
if (member(item, curset))
389+
return length(curset) - 1;
390+
}
391+
return 0;
392+
}
393+
369394
/****************************************************************************
370395
* PATHKEY COMPARISONS
371396
****************************************************************************/
@@ -597,6 +622,9 @@ get_cheapest_fractional_path_for_pathkeys(List *paths,
597622
*
598623
* If 'scandir' is BackwardScanDirection, attempt to build pathkeys
599624
* representing a backwards scan of the index. Return NIL if can't do it.
625+
*
626+
* We generate the full pathkeys list whether or not all are useful for the
627+
* current query. Caller should do truncate_useless_pathkeys().
600628
*/
601629
List *
602630
build_index_pathkeys(Query *root,
@@ -699,9 +727,10 @@ find_indexkey_var(Query *root, RelOptInfo *rel, AttrNumber varattno)
699727

700728
foreach(temp, rel->targetlist)
701729
{
702-
Var *tle_var = get_expr(lfirst(temp));
730+
Var *tle_var = (Var *) ((TargetEntry *) lfirst(temp))->expr;
703731

704-
if (IsA(tle_var, Var) &&tle_var->varattno == varattno)
732+
if (IsA(tle_var, Var) &&
733+
tle_var->varattno == varattno)
705734
return tle_var;
706735
}
707736

@@ -714,6 +743,112 @@ find_indexkey_var(Query *root, RelOptInfo *rel, AttrNumber varattno)
714743
return makeVar(relid, varattno, vartypeid, type_mod, 0);
715744
}
716745

746+
/*
747+
* build_subquery_pathkeys
748+
* Build a pathkeys list that describes the ordering of a subquery's
749+
* result (in the terms of the outer query). The subquery must already
750+
* have been planned, so that its query_pathkeys field has been set.
751+
*
752+
* It is not necessary for caller to do truncate_useless_pathkeys(),
753+
* because we select keys in a way that takes usefulness of the keys into
754+
* account.
755+
*/
756+
List *
757+
build_subquery_pathkeys(Query *root, RelOptInfo *rel, Query *subquery)
758+
{
759+
List *retval = NIL;
760+
int retvallen = 0;
761+
int outer_query_keys = length(root->query_pathkeys);
762+
List *l;
763+
764+
foreach(l, subquery->query_pathkeys)
765+
{
766+
List *sub_pathkey = (List *) lfirst(l);
767+
List *j;
768+
PathKeyItem *best_item = NULL;
769+
int best_score = 0;
770+
List *cpathkey;
771+
772+
/*
773+
* The sub_pathkey could contain multiple elements (representing
774+
* knowledge that multiple items are effectively equal). Each
775+
* element might match none, one, or more of the output columns
776+
* that are visible to the outer query. This means we may have
777+
* multiple possible representations of the sub_pathkey in the
778+
* context of the outer query. Ideally we would generate them all
779+
* and put them all into a pathkey list of the outer query, thereby
780+
* propagating equality knowledge up to the outer query. Right now
781+
* we cannot do so, because the outer query's canonical pathkey
782+
* sets are already frozen when this is called. Instead we prefer
783+
* the one that has the highest "score" (number of canonical pathkey
784+
* peers, plus one if it matches the outer query_pathkeys).
785+
* This is the most likely to be useful in the outer query.
786+
*/
787+
foreach(j, sub_pathkey)
788+
{
789+
PathKeyItem *sub_item = (PathKeyItem *) lfirst(j);
790+
Node *sub_key = sub_item->key;
791+
List *k;
792+
793+
foreach(k, subquery->targetList)
794+
{
795+
TargetEntry *tle = (TargetEntry *) lfirst(k);
796+
797+
if (!tle->resdom->resjunk &&
798+
equal(tle->expr, sub_key))
799+
{
800+
/* Found a representation for this sub_key */
801+
Var *outer_var;
802+
PathKeyItem *outer_item;
803+
int score;
804+
805+
outer_var = makeVar(rel->relid,
806+
tle->resdom->resno,
807+
tle->resdom->restype,
808+
tle->resdom->restypmod,
809+
0);
810+
outer_item = makePathKeyItem((Node *) outer_var,
811+
sub_item->sortop);
812+
/* score = # of mergejoin peers */
813+
score = count_canonical_peers(root, outer_item);
814+
/* +1 if it matches the proper query_pathkeys item */
815+
if (retvallen < outer_query_keys &&
816+
member(outer_item,
817+
nth(retvallen, root->query_pathkeys)))
818+
score++;
819+
if (score > best_score)
820+
{
821+
best_item = outer_item;
822+
best_score = score;
823+
}
824+
}
825+
}
826+
}
827+
828+
/*
829+
* If we couldn't find a representation of this sub_pathkey,
830+
* we're done (we can't use the ones to its right, either).
831+
*/
832+
if (!best_item)
833+
break;
834+
835+
/* Canonicalize the chosen item (we did not before) */
836+
cpathkey = make_canonical_pathkey(root, best_item);
837+
838+
/*
839+
* Eliminate redundant ordering info; could happen if outer
840+
* query equijoins subquery keys...
841+
*/
842+
if (!ptrMember(cpathkey, retval))
843+
{
844+
retval = lappend(retval, cpathkey);
845+
retvallen++;
846+
}
847+
}
848+
849+
return retval;
850+
}
851+
717852
/*
718853
* build_join_pathkeys
719854
* Build the path keys for a join relation constructed by mergejoin or

‎src/backend/optimizer/plan/planner.c

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.146 2003/02/09 23:57:19 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.147 2003/02/15 20:12:40 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -469,6 +469,9 @@ inheritance_planner(Query *parse, List *inheritlist)
469469
/* Save the target-relations list for the executor, too */
470470
parse->resultRelations = inheritlist;
471471

472+
/* Mark result as unordered (probably unnecessary) */
473+
parse->query_pathkeys = NIL;
474+
472475
return (Plan *) make_append(subplans, true, tlist);
473476
}
474477

@@ -491,7 +494,8 @@ inheritance_planner(Query *parse, List *inheritlist)
491494
* The normal case is to pass -1, but some callers pass values >= 0 to
492495
* override this routine's determination of the appropriate fraction.
493496
*
494-
* Returns a query plan.
497+
* Returns a query plan. Also, parse->query_pathkeys is returned as the
498+
* actual output ordering of the plan (in pathkey format).
495499
*--------------------
496500
*/
497501
static Plan *
@@ -1191,10 +1195,13 @@ grouping_planner(Query *parse, double tuple_fraction)
11911195
if (parse->sortClause)
11921196
{
11931197
if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys))
1198+
{
11941199
result_plan = (Plan *) make_sort_from_sortclauses(parse,
11951200
tlist,
11961201
result_plan,
11971202
parse->sortClause);
1203+
current_pathkeys = sort_pathkeys;
1204+
}
11981205
}
11991206

12001207
/*
@@ -1232,6 +1239,12 @@ grouping_planner(Query *parse, double tuple_fraction)
12321239
parse->limitCount);
12331240
}
12341241

1242+
/*
1243+
* Return the actual output ordering in query_pathkeys for possible
1244+
* use by an outer query level.
1245+
*/
1246+
parse->query_pathkeys = current_pathkeys;
1247+
12351248
return result_plan;
12361249
}
12371250

‎src/backend/optimizer/util/pathnode.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.87 2003/02/08 20:20:55 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.88 2003/02/15 20:12:40 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -676,13 +676,13 @@ hash_safe_tlist(List *tlist)
676676
* returning the pathnode.
677677
*/
678678
Path *
679-
create_subqueryscan_path(RelOptInfo *rel)
679+
create_subqueryscan_path(RelOptInfo *rel, List *pathkeys)
680680
{
681681
Path *pathnode = makeNode(Path);
682682

683683
pathnode->pathtype = T_SubqueryScan;
684684
pathnode->parent = rel;
685-
pathnode->pathkeys = NIL; /* for now, assume unordered result */
685+
pathnode->pathkeys = pathkeys;
686686

687687
/* just copy the subplan's cost estimates */
688688
pathnode->startup_cost = rel->subplan->startup_cost;

‎src/backend/optimizer/util/relnode.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.47 2003/02/08 20:20:55 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.48 2003/02/15 20:12:40 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -381,11 +381,11 @@ new_join_tlist(List *tlist,
381381

382382
foreach(i, tlist)
383383
{
384-
TargetEntry *xtl = lfirst(i);
384+
TargetEntry *tle = lfirst(i);
385385

386386
resdomno += 1;
387387
t_list = lappend(t_list,
388-
create_tl_element(get_expr(xtl), resdomno));
388+
create_tl_element((Var *) tle->expr, resdomno));
389389
}
390390

391391
return t_list;

‎src/backend/optimizer/util/tlist.c

Lines changed: 1 addition & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/tlist.c,v 1.54 2003/01/20 18:54:57 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/tlist.c,v 1.55 2003/02/15 20:12:40 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -204,15 +204,6 @@ add_to_flat_tlist(List *tlist, List *vars)
204204
return tlist;
205205
}
206206

207-
Var *
208-
get_expr(TargetEntry *tle)
209-
{
210-
Assert(tle != NULL);
211-
Assert(tle->expr != NULL);
212-
213-
return (Var *) tle->expr;
214-
}
215-
216207
/*
217208
* get_sortgroupclause_tle
218209
* Find the targetlist entry matching the given SortClause

‎src/include/optimizer/pathnode.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: pathnode.h,v 1.49 2003/02/08 20:20:55 tgl Exp $
10+
* $Id: pathnode.h,v 1.50 2003/02/15 20:12:41 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -41,7 +41,7 @@ extern ResultPath *create_result_path(RelOptInfo *rel, Path *subpath,
4141
extern MaterialPath *create_material_path(RelOptInfo *rel, Path *subpath);
4242
extern UniquePath *create_unique_path(Query *root, RelOptInfo *rel,
4343
Path *subpath);
44-
extern Path *create_subqueryscan_path(RelOptInfo *rel);
44+
extern Path *create_subqueryscan_path(RelOptInfo *rel, List *pathkeys);
4545
extern Path *create_functionscan_path(Query *root, RelOptInfo *rel);
4646

4747
extern NestPath *create_nestloop_path(Query *root,

‎src/include/optimizer/paths.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
99
* Portions Copyright (c) 1994, Regents of the University of California
1010
*
11-
* $Id: paths.h,v 1.65 2003/01/25 23:10:30 tgl Exp $
11+
* $Id: paths.h,v 1.66 2003/02/15 20:12:41 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -104,6 +104,8 @@ extern Path *get_cheapest_fractional_path_for_pathkeys(List *paths,
104104
extern List *build_index_pathkeys(Query *root, RelOptInfo *rel,
105105
IndexOptInfo *index,
106106
ScanDirection scandir);
107+
extern List *build_subquery_pathkeys(Query *root, RelOptInfo *rel,
108+
Query *subquery);
107109
extern List *build_join_pathkeys(Query *root,
108110
RelOptInfo *joinrel,
109111
List *outer_pathkeys);

‎src/include/optimizer/tlist.h

Lines changed: 1 addition & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: tlist.h,v 1.33 2003/01/20 18:55:06 tgl Exp $
10+
* $Id: tlist.h,v 1.34 2003/02/15 20:12:41 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -26,8 +26,6 @@ extern List *new_unsorted_tlist(List *targetlist);
2626
extern List *flatten_tlist(List *tlist);
2727
extern List *add_to_flat_tlist(List *tlist, List *vars);
2828

29-
extern Var *get_expr(TargetEntry *tle);
30-
3129
extern TargetEntry *get_sortgroupclause_tle(SortClause *sortClause,
3230
List *targetList);
3331
extern Node *get_sortgroupclause_expr(SortClause *sortClause,

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