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Commit 0927d2f

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robertmhaasrobertmhaas
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Let Parallel Append over simple UNION ALL have partial subpaths.
A simple UNION ALL gets flattened into an appendrel of subquery RTEs, but up until now it's been impossible for the appendrel to use the partial paths for the subqueries, so we can implement the appendrel as a Parallel Append but only one with non-partial paths as children. There are three separate obstacles to removing that limitation. First, when planning a subquery, propagate any partial paths to the final_rel so that they are potentially visible to outer query levels (but not if they have initPlans attached, because that wouldn't be safe). Second, after planning a subquery, propagate any partial paths for the final_rel to the subquery RTE in the outer query level in the same way we do for non-partial paths. Third, teach finalize_plan() to account for the possibility that the fake parameter we use for rescan signalling when the plan contains a Gather (Merge) node may be propagated from an outer query level. Patch by me, reviewed and tested by Amit Khandekar, Rajkumar Raghuwanshi, and Ashutosh Bapat. Test cases based on examples by Rajkumar Raghuwanshi. Discussion: http://postgr.es/m/CA+Tgmoa6L9A1nNCk3aTDVZLZ4KkHDn1+tm7mFyFvP+uQPS7bAg@mail.gmail.com
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‎src/backend/optimizer/path/allpaths.c

Copy file name to clipboardExpand all lines: src/backend/optimizer/path/allpaths.c
+22Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2179,6 +2179,28 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
21792179
create_subqueryscan_path(root, rel, subpath,
21802180
pathkeys, required_outer));
21812181
}
2182+
2183+
/* If consider_parallel is false, there should be no partial paths. */
2184+
Assert(sub_final_rel->consider_parallel ||
2185+
sub_final_rel->partial_pathlist == NIL);
2186+
2187+
/* Same for partial paths. */
2188+
foreach(lc, sub_final_rel->partial_pathlist)
2189+
{
2190+
Path *subpath = (Path *) lfirst(lc);
2191+
List *pathkeys;
2192+
2193+
/* Convert subpath's pathkeys to outer representation */
2194+
pathkeys = convert_subquery_pathkeys(root,
2195+
rel,
2196+
subpath->pathkeys,
2197+
make_tlist_from_pathtarget(subpath->pathtarget));
2198+
2199+
/* Generate outer path using this subpath */
2200+
add_partial_path(rel, (Path *)
2201+
create_subqueryscan_path(root, rel, subpath,
2202+
pathkeys, required_outer));
2203+
}
21822204
}
21832205

21842206
/*

‎src/backend/optimizer/plan/planner.c

Copy file name to clipboardExpand all lines: src/backend/optimizer/plan/planner.c
+16Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2194,6 +2194,22 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
21942194
add_path(final_rel, path);
21952195
}
21962196

2197+
/*
2198+
* Generate partial paths for final_rel, too, if outer query levels might
2199+
* be able to make use of them.
2200+
*/
2201+
if (final_rel->consider_parallel && root->query_level > 1 &&
2202+
!limit_needed(parse))
2203+
{
2204+
Assert(!parse->rowMarks && parse->commandType == CMD_SELECT);
2205+
foreach(lc, current_rel->partial_pathlist)
2206+
{
2207+
Path *partial_path = (Path *) lfirst(lc);
2208+
2209+
add_partial_path(final_rel, partial_path);
2210+
}
2211+
}
2212+
21972213
/*
21982214
* If there is an FDW that's responsible for all baserels of the query,
21992215
* let it consider adding ForeignPaths.

‎src/backend/optimizer/plan/subselect.c

Copy file name to clipboardExpand all lines: src/backend/optimizer/plan/subselect.c
+15-2Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2202,6 +2202,13 @@ SS_charge_for_initplans(PlannerInfo *root, RelOptInfo *final_rel)
22022202
path->parallel_safe = false;
22032203
}
22042204

2205+
/*
2206+
* Forget about any partial paths and clear consider_parallel, too;
2207+
* they're not usable if we attached an initPlan.
2208+
*/
2209+
final_rel->partial_pathlist = NIL;
2210+
final_rel->consider_parallel = false;
2211+
22052212
/* We needn't do set_cheapest() here, caller will do it */
22062213
}
22072214

@@ -2407,10 +2414,16 @@ finalize_plan(PlannerInfo *root, Plan *plan,
24072414
{
24082415
SubqueryScan *sscan = (SubqueryScan *) plan;
24092416
RelOptInfo *rel;
2417+
Bitmapset *subquery_params;
24102418

2411-
/* We must run SS_finalize_plan on the subquery */
2419+
/* We must run finalize_plan on the subquery */
24122420
rel = find_base_rel(root, sscan->scan.scanrelid);
2413-
SS_finalize_plan(rel->subroot, sscan->subplan);
2421+
subquery_params = rel->subroot->outer_params;
2422+
if (gather_param >= 0)
2423+
subquery_params = bms_add_member(bms_copy(subquery_params),
2424+
gather_param);
2425+
finalize_plan(rel->subroot, sscan->subplan, gather_param,
2426+
subquery_params, NULL);
24142427

24152428
/* Now we can add its extParams to the parent's params */
24162429
context.paramids = bms_add_members(context.paramids,

‎src/test/regress/expected/select_parallel.out

Copy file name to clipboardExpand all lines: src/test/regress/expected/select_parallel.out
+65Lines changed: 65 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -890,4 +890,69 @@ select stringu1::int2 from tenk1 where unique1 = 1;
890890
ERROR: invalid input syntax for integer: "BAAAAA"
891891
CONTEXT: parallel worker
892892
ROLLBACK TO SAVEPOINT settings;
893+
-- test interaction with set-returning functions
894+
SAVEPOINT settings;
895+
-- multiple subqueries under a single Gather node
896+
-- must set parallel_setup_cost > 0 to discourage multiple Gather nodes
897+
SET LOCAL parallel_setup_cost = 10;
898+
EXPLAIN (COSTS OFF)
899+
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1
900+
UNION ALL
901+
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1;
902+
QUERY PLAN
903+
----------------------------------------------------
904+
Gather
905+
Workers Planned: 4
906+
-> Parallel Append
907+
-> Parallel Seq Scan on tenk1
908+
Filter: (fivethous = (tenthous + 1))
909+
-> Parallel Seq Scan on tenk1 tenk1_1
910+
Filter: (fivethous = (tenthous + 1))
911+
(7 rows)
912+
913+
ROLLBACK TO SAVEPOINT settings;
914+
-- can't use multiple subqueries under a single Gather node due to initPlans
915+
EXPLAIN (COSTS OFF)
916+
SELECT unique1 FROM tenk1 WHERE fivethous =
917+
(SELECT unique1 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
918+
UNION ALL
919+
SELECT unique1 FROM tenk1 WHERE fivethous =
920+
(SELECT unique2 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
921+
ORDER BY 1;
922+
QUERY PLAN
923+
--------------------------------------------------------------------
924+
Sort
925+
Sort Key: tenk1.unique1
926+
-> Append
927+
-> Gather
928+
Workers Planned: 4
929+
Params Evaluated: $1
930+
InitPlan 1 (returns $1)
931+
-> Limit
932+
-> Gather
933+
Workers Planned: 4
934+
-> Parallel Seq Scan on tenk1 tenk1_2
935+
Filter: (fivethous = 1)
936+
-> Parallel Seq Scan on tenk1
937+
Filter: (fivethous = $1)
938+
-> Gather
939+
Workers Planned: 4
940+
Params Evaluated: $3
941+
InitPlan 2 (returns $3)
942+
-> Limit
943+
-> Gather
944+
Workers Planned: 4
945+
-> Parallel Seq Scan on tenk1 tenk1_3
946+
Filter: (fivethous = 1)
947+
-> Parallel Seq Scan on tenk1 tenk1_1
948+
Filter: (fivethous = $3)
949+
(25 rows)
950+
951+
-- test interaction with SRFs
952+
SELECT * FROM information_schema.foreign_data_wrapper_options
953+
ORDER BY 1, 2, 3;
954+
foreign_data_wrapper_catalog | foreign_data_wrapper_name | option_name | option_value
955+
------------------------------+---------------------------+-------------+--------------
956+
(0 rows)
957+
893958
rollback;

‎src/test/regress/sql/select_parallel.sql

Copy file name to clipboardExpand all lines: src/test/regress/sql/select_parallel.sql
+25Lines changed: 25 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -358,4 +358,29 @@ SET LOCAL force_parallel_mode = 1;
358358
select stringu1::int2 from tenk1 where unique1 = 1;
359359
ROLLBACK TO SAVEPOINT settings;
360360

361+
-- test interaction with set-returning functions
362+
SAVEPOINT settings;
363+
364+
-- multiple subqueries under a single Gather node
365+
-- must set parallel_setup_cost > 0 to discourage multiple Gather nodes
366+
SET LOCAL parallel_setup_cost = 10;
367+
EXPLAIN (COSTS OFF)
368+
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1
369+
UNION ALL
370+
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1;
371+
ROLLBACK TO SAVEPOINT settings;
372+
373+
-- can't use multiple subqueries under a single Gather node due to initPlans
374+
EXPLAIN (COSTS OFF)
375+
SELECT unique1 FROM tenk1 WHERE fivethous =
376+
(SELECT unique1 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
377+
UNION ALL
378+
SELECT unique1 FROM tenk1 WHERE fivethous =
379+
(SELECT unique2 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
380+
ORDER BY 1;
381+
382+
-- test interaction with SRFs
383+
SELECT * FROM information_schema.foreign_data_wrapper_options
384+
ORDER BY 1, 2, 3;
385+
361386
rollback;

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