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Commit6e2c762

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Fix generation of MergeAppend plans for optimized min/max on expressions.
Before jamming a desired targetlist into a plan node, one really ought tomake sure the plan node can handle projections, and insert a bufferingResult plan node if not. planagg.c forgot to do this, which is a hangoverfrom the days when it only dealt with IndexScan plan types. MergeAppenddoesn't project though, not to mention that it gets unhappy if you removeits possibly-resjunk sort columns. The code accidentally failed to failfor cases in which the min/max argument was a simple Var, because the newtargetlist would be equivalent to the original "flat" tlist anyway.For any more complex case, it's been broken since 9.1 where we introducedthe ability to optimize min/max using MergeAppend, as reported by RaphaelBauduin. Fix by duplicating the logic from grouping_planner that decideswhether we need a Result node.In 9.2 and 9.1, this requires back-porting the tlist_same_exprs() functionintroduced in commit4387cf9, else we'duselessly add a Result node in cases that worked before. It's rathertempting to back-patch that whole commit so that we can avoid extra Resultnodes in mainline cases too; but I'll refrain, since that code hasn'treally seen all that much field testing yet.
1 parentaad87e3 commit6e2c762

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5 files changed

+123
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lines changed

5 files changed

+123
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lines changed

‎src/backend/optimizer/plan/planagg.c

Lines changed: 22 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,7 @@
3737
#include"optimizer/paths.h"
3838
#include"optimizer/planmain.h"
3939
#include"optimizer/subselect.h"
40+
#include"optimizer/tlist.h"
4041
#include"parser/parsetree.h"
4142
#include"parser/parse_clause.h"
4243
#include"utils/lsyscache.h"
@@ -521,7 +522,27 @@ make_agg_subplan(PlannerInfo *root, MinMaxAggInfo *mminfo)
521522
*/
522523
plan=create_plan(subroot,mminfo->path);
523524

524-
plan->targetlist=subparse->targetList;
525+
/*
526+
* If the top-level plan node is one that cannot do expression evaluation
527+
* and its existing target list isn't already what we need, we must insert
528+
* a Result node to project the desired tlist.
529+
*/
530+
if (!is_projection_capable_plan(plan)&&
531+
!tlist_same_exprs(subparse->targetList,plan->targetlist))
532+
{
533+
plan= (Plan*)make_result(subroot,
534+
subparse->targetList,
535+
NULL,
536+
plan);
537+
}
538+
else
539+
{
540+
/*
541+
* Otherwise, just replace the subplan's flat tlist with the desired
542+
* tlist.
543+
*/
544+
plan->targetlist=subparse->targetList;
545+
}
525546

526547
plan= (Plan*)make_limit(plan,
527548
subparse->limitOffset,

‎src/backend/optimizer/util/tlist.c

Lines changed: 37 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -188,6 +188,43 @@ get_tlist_exprs(List *tlist, bool includeJunk)
188188
}
189189

190190

191+
/*
192+
* tlist_same_exprs
193+
*Check whether two target lists contain the same expressions
194+
*
195+
* Note: this function is used to decide whether it's safe to jam a new tlist
196+
* into a non-projection-capable plan node. Obviously we can't do that unless
197+
* the node's tlist shows it already returns the column values we want.
198+
* However, we can ignore the TargetEntry attributes resname, ressortgroupref,
199+
* resorigtbl, resorigcol, and resjunk, because those are only labelings that
200+
* don't affect the row values computed by the node. (Moreover, if we didn't
201+
* ignore them, we'd frequently fail to make the desired optimization, since
202+
* the planner tends to not bother to make resname etc. valid in intermediate
203+
* plan nodes.) Note that on success, the caller must still jam the desired
204+
* tlist into the plan node, else it won't have the desired labeling fields.
205+
*/
206+
bool
207+
tlist_same_exprs(List*tlist1,List*tlist2)
208+
{
209+
ListCell*lc1,
210+
*lc2;
211+
212+
if (list_length(tlist1)!=list_length(tlist2))
213+
return false;/* not same length, so can't match */
214+
215+
forboth(lc1,tlist1,lc2,tlist2)
216+
{
217+
TargetEntry*tle1= (TargetEntry*)lfirst(lc1);
218+
TargetEntry*tle2= (TargetEntry*)lfirst(lc2);
219+
220+
if (!equal(tle1->expr,tle2->expr))
221+
return false;
222+
}
223+
224+
return true;
225+
}
226+
227+
191228
/*
192229
* Does tlist have same output datatypes as listed in colTypes?
193230
*

‎src/include/optimizer/tlist.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,9 @@ extern List *flatten_tlist(List *tlist, PVCAggregateBehavior aggbehavior,
2626
externList*add_to_flat_tlist(List*tlist,List*exprs);
2727

2828
externList*get_tlist_exprs(List*tlist,boolincludeJunk);
29+
30+
externbooltlist_same_exprs(List*tlist1,List*tlist2);
31+
2932
externbooltlist_same_datatypes(List*tlist,List*colTypes,booljunkOK);
3033
externbooltlist_same_collations(List*tlist,List*colCollations,booljunkOK);
3134

‎src/test/regress/expected/inherit.out

Lines changed: 57 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1203,6 +1203,28 @@ select * from matest0 order by 1-id;
12031203
1 | Test 1
12041204
(6 rows)
12051205

1206+
explain (verbose, costs off) select min(1-id) from matest0;
1207+
QUERY PLAN
1208+
------------------------------------------------
1209+
Aggregate
1210+
Output: min((1 - public.matest0.id))
1211+
-> Append
1212+
-> Seq Scan on public.matest0
1213+
Output: public.matest0.id
1214+
-> Seq Scan on public.matest1 matest0
1215+
Output: public.matest0.id
1216+
-> Seq Scan on public.matest2 matest0
1217+
Output: public.matest0.id
1218+
-> Seq Scan on public.matest3 matest0
1219+
Output: public.matest0.id
1220+
(11 rows)
1221+
1222+
select min(1-id) from matest0;
1223+
min
1224+
-----
1225+
-5
1226+
(1 row)
1227+
12061228
reset enable_indexscan;
12071229
set enable_seqscan = off; -- plan with fewest seqscans should be merge
12081230
explain (verbose, costs off) select * from matest0 order by 1-id;
@@ -1236,6 +1258,41 @@ select * from matest0 order by 1-id;
12361258
1 | Test 1
12371259
(6 rows)
12381260

1261+
explain (verbose, costs off) select min(1-id) from matest0;
1262+
QUERY PLAN
1263+
--------------------------------------------------------------------------------------
1264+
Result
1265+
Output: $0
1266+
InitPlan 1 (returns $0)
1267+
-> Limit
1268+
Output: ((1 - public.matest0.id))
1269+
-> Result
1270+
Output: ((1 - public.matest0.id))
1271+
-> Merge Append
1272+
Sort Key: ((1 - public.matest0.id))
1273+
-> Index Scan using matest0i on public.matest0
1274+
Output: public.matest0.id, (1 - public.matest0.id)
1275+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1276+
-> Index Scan using matest1i on public.matest1 matest0
1277+
Output: public.matest0.id, (1 - public.matest0.id)
1278+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1279+
-> Sort
1280+
Output: public.matest0.id, ((1 - public.matest0.id))
1281+
Sort Key: ((1 - public.matest0.id))
1282+
-> Seq Scan on public.matest2 matest0
1283+
Output: public.matest0.id, (1 - public.matest0.id)
1284+
Filter: ((1 - public.matest0.id) IS NOT NULL)
1285+
-> Index Scan using matest3i on public.matest3 matest0
1286+
Output: public.matest0.id, (1 - public.matest0.id)
1287+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1288+
(24 rows)
1289+
1290+
select min(1-id) from matest0;
1291+
min
1292+
-----
1293+
-5
1294+
(1 row)
1295+
12391296
reset enable_seqscan;
12401297
drop table matest0 cascade;
12411298
NOTICE: drop cascades to 3 other objects

‎src/test/regress/sql/inherit.sql

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -398,11 +398,15 @@ insert into matest3 (name) values ('Test 6');
398398
set enable_indexscan= off;-- force use of seqscan/sort, so no merge
399399
explain (verbose, costs off)select*from matest0order by1-id;
400400
select*from matest0order by1-id;
401+
explain (verbose, costs off)selectmin(1-id)from matest0;
402+
selectmin(1-id)from matest0;
401403
reset enable_indexscan;
402404

403405
set enable_seqscan= off;-- plan with fewest seqscans should be merge
404406
explain (verbose, costs off)select*from matest0order by1-id;
405407
select*from matest0order by1-id;
408+
explain (verbose, costs off)selectmin(1-id)from matest0;
409+
selectmin(1-id)from matest0;
406410
reset enable_seqscan;
407411

408412
droptable matest0 cascade;

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