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Commitaa8a2c3

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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 parent74aea2a commitaa8a2c3

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5 files changed

+124
-1
lines changed

5 files changed

+124
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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
@@ -38,6 +38,7 @@
3838
#include"optimizer/planmain.h"
3939
#include"optimizer/planner.h"
4040
#include"optimizer/subselect.h"
41+
#include"optimizer/tlist.h"
4142
#include"parser/parsetree.h"
4243
#include"parser/parse_clause.h"
4344
#include"utils/lsyscache.h"
@@ -525,7 +526,27 @@ make_agg_subplan(PlannerInfo *root, MinMaxAggInfo *mminfo)
525526
*/
526527
plan=create_plan(subroot,mminfo->path);
527528

528-
plan->targetlist=subparse->targetList;
529+
/*
530+
* If the top-level plan node is one that cannot do expression evaluation
531+
* and its existing target list isn't already what we need, we must insert
532+
* a Result node to project the desired tlist.
533+
*/
534+
if (!is_projection_capable_plan(plan)&&
535+
!tlist_same_exprs(subparse->targetList,plan->targetlist))
536+
{
537+
plan= (Plan*)make_result(subroot,
538+
subparse->targetList,
539+
NULL,
540+
plan);
541+
}
542+
else
543+
{
544+
/*
545+
* Otherwise, just replace the subplan's flat tlist with the desired
546+
* tlist.
547+
*/
548+
plan->targetlist=subparse->targetList;
549+
}
529550

530551
plan= (Plan*)make_limit(plan,
531552
subparse->limitOffset,

‎src/backend/optimizer/util/tlist.c

Lines changed: 37 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -187,6 +187,43 @@ get_tlist_exprs(List *tlist, bool includeJunk)
187187
}
188188

189189

190+
/*
191+
* tlist_same_exprs
192+
*Check whether two target lists contain the same expressions
193+
*
194+
* Note: this function is used to decide whether it's safe to jam a new tlist
195+
* into a non-projection-capable plan node. Obviously we can't do that unless
196+
* the node's tlist shows it already returns the column values we want.
197+
* However, we can ignore the TargetEntry attributes resname, ressortgroupref,
198+
* resorigtbl, resorigcol, and resjunk, because those are only labelings that
199+
* don't affect the row values computed by the node. (Moreover, if we didn't
200+
* ignore them, we'd frequently fail to make the desired optimization, since
201+
* the planner tends to not bother to make resname etc. valid in intermediate
202+
* plan nodes.) Note that on success, the caller must still jam the desired
203+
* tlist into the plan node, else it won't have the desired labeling fields.
204+
*/
205+
bool
206+
tlist_same_exprs(List*tlist1,List*tlist2)
207+
{
208+
ListCell*lc1,
209+
*lc2;
210+
211+
if (list_length(tlist1)!=list_length(tlist2))
212+
return false;/* not same length, so can't match */
213+
214+
forboth(lc1,tlist1,lc2,tlist2)
215+
{
216+
TargetEntry*tle1= (TargetEntry*)lfirst(lc1);
217+
TargetEntry*tle2= (TargetEntry*)lfirst(lc2);
218+
219+
if (!equal(tle1->expr,tle2->expr))
220+
return false;
221+
}
222+
223+
return true;
224+
}
225+
226+
190227
/*
191228
* Does tlist have same output datatypes as listed in colTypes?
192229
*

‎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: 58 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1216,6 +1216,28 @@ select * from matest0 order by 1-id;
12161216
1 | Test 1
12171217
(6 rows)
12181218

1219+
explain (verbose, costs off) select min(1-id) from matest0;
1220+
QUERY PLAN
1221+
------------------------------------------------
1222+
Aggregate
1223+
Output: min((1 - public.matest0.id))
1224+
-> Append
1225+
-> Seq Scan on public.matest0
1226+
Output: public.matest0.id
1227+
-> Seq Scan on public.matest1 matest0
1228+
Output: public.matest0.id
1229+
-> Seq Scan on public.matest2 matest0
1230+
Output: public.matest0.id
1231+
-> Seq Scan on public.matest3 matest0
1232+
Output: public.matest0.id
1233+
(11 rows)
1234+
1235+
select min(1-id) from matest0;
1236+
min
1237+
-----
1238+
-5
1239+
(1 row)
1240+
12191241
reset enable_indexscan;
12201242
set enable_seqscan = off; -- plan with fewest seqscans should be merge
12211243
explain (verbose, costs off) select * from matest0 order by 1-id;
@@ -1249,6 +1271,42 @@ select * from matest0 order by 1-id;
12491271
1 | Test 1
12501272
(6 rows)
12511273

1274+
explain (verbose, costs off) select min(1-id) from matest0;
1275+
QUERY PLAN
1276+
--------------------------------------------------------------------------------------
1277+
Result
1278+
Output: $0
1279+
InitPlan 1 (returns $0)
1280+
-> Limit
1281+
Output: ((1 - public.matest0.id))
1282+
-> Result
1283+
Output: ((1 - public.matest0.id))
1284+
-> Merge Append
1285+
Sort Key: ((1 - public.matest0.id))
1286+
-> Index Scan using matest0i on public.matest0
1287+
Output: public.matest0.id, (1 - public.matest0.id)
1288+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1289+
-> Index Scan using matest1i on public.matest1 matest0
1290+
Output: public.matest0.id, (1 - public.matest0.id)
1291+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1292+
-> Sort
1293+
Output: public.matest0.id, ((1 - public.matest0.id))
1294+
Sort Key: ((1 - public.matest0.id))
1295+
-> Bitmap Heap Scan on public.matest2 matest0
1296+
Output: public.matest0.id, (1 - public.matest0.id)
1297+
Filter: ((1 - public.matest0.id) IS NOT NULL)
1298+
-> Bitmap Index Scan on matest2_pkey
1299+
-> Index Scan using matest3i on public.matest3 matest0
1300+
Output: public.matest0.id, (1 - public.matest0.id)
1301+
Index Cond: ((1 - public.matest0.id) IS NOT NULL)
1302+
(25 rows)
1303+
1304+
select min(1-id) from matest0;
1305+
min
1306+
-----
1307+
-5
1308+
(1 row)
1309+
12521310
reset enable_seqscan;
12531311
drop table matest0 cascade;
12541312
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
@@ -382,11 +382,15 @@ insert into matest3 (name) values ('Test 6');
382382
set enable_indexscan= off;-- force use of seqscan/sort, so no merge
383383
explain (verbose, costs off)select*from matest0order by1-id;
384384
select*from matest0order by1-id;
385+
explain (verbose, costs off)selectmin(1-id)from matest0;
386+
selectmin(1-id)from matest0;
385387
reset enable_indexscan;
386388

387389
set enable_seqscan= off;-- plan with fewest seqscans should be merge
388390
explain (verbose, costs off)select*from matest0order by1-id;
389391
select*from matest0order by1-id;
392+
explain (verbose, costs off)selectmin(1-id)from matest0;
393+
selectmin(1-id)from matest0;
390394
reset enable_seqscan;
391395

392396
droptable matest0 cascade;

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