Tom Lane wrote:
> Alvaro Herrera <alvhe...@alvh.no-ip.org> writes:
> > Tom Lane wrote:
> >> It seems quite silly to be asking for a parallel plan and then insisting
> >> it not run in parallel.
>
> > Now that you mention it, this probably decreases coverage for the
> > choose_next_subplan_for_worker function.
>
> Yeah, loss of executor code coverage was what concerned me.
Here's a proposed patch for this.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
commit e8ec68c15788edd8dc01463fc2df9526faab4bdc[m
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
AuthorDate: Mon Apr 16 16:54:41 2018 -0300
CommitDate: Mon Apr 16 17:42:53 2018 -0300
Restore partition_prune's usage of parallel workers
This reverts commit 4d0f6d3f207d ("Attempt to stabilize partition_prune
test output (2)"), and attempts to stabilize the test by using string
replacement to hide any loop count difference in parallel nodes.
Discussion: https://postgr.es/m/4475.1523628...@sss.pgh.pa.us
diff --git a/src/test/regress/expected/partition_prune.out
b/src/test/regress/expected/partition_prune.out
index 41d38d3d9a..49a46fa69f 100644
--- a/src/test/regress/expected/partition_prune.out
+++ b/src/test/regress/expected/partition_prune.out
@@ -1748,16 +1748,34 @@ explain (analyze, costs off, summary off, timing off)
execute ab_q3 (2, 2);
(10 rows)
-- Parallel append
+-- Suppress the number of loops each node runs for. This is because workers
+-- may run a parallel node more than once, if timing conditions are just so,
+-- which destabilizes the test.
+create function explain_parallel_append(text, int[]) returns setof text
+language plpgsql as
+$$
+declare
+ ln text;
+ args text := string_agg(u::text, ', ') from unnest($2) u;
+begin
+ for ln in
+ execute format('explain (analyze, costs off, summary off, timing off)
execute %s(%s)',
+ $1, args)
+ loop
+ if ln like '%Parallel%' then
+ ln := regexp_replace(ln, 'loops=\d*', 'loops=N');
+ end if;
+ return next ln;
+ end loop;
+end;
+$$;
prepare ab_q4 (int, int) as
select avg(a) from ab where a between $1 and $2 and b < 4;
-- Encourage use of parallel plans
set parallel_setup_cost = 0;
set parallel_tuple_cost = 0;
set min_parallel_table_scan_size = 0;
--- set this so we get a parallel plan
set max_parallel_workers_per_gather = 2;
--- and zero this so that workers don't destabilize the explain output
-set max_parallel_workers = 0;
-- Execute query 5 times to allow choose_custom_plan
-- to start considering a generic plan.
execute ab_q4 (1, 8);
@@ -1790,21 +1808,21 @@ execute ab_q4 (1, 8);
(1 row)
-explain (analyze, costs off, summary off, timing off) execute ab_q4 (2, 2);
- QUERY PLAN
+select explain_parallel_append('ab_q4', '{2, 2}');
+ explain_parallel_append
-------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=3 loops=1)
Workers Planned: 2
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Parallel Append (actual rows=0 loops=1)
+ Workers Launched: 2
+ -> Partial Aggregate (actual rows=1 loops=3)
+ -> Parallel Append (actual rows=0 loops=N)
Subplans Removed: 6
- -> Parallel Seq Scan on ab_a2_b1 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b1 (actual rows=0 loops=N)
Filter: ((a >= $1) AND (a <= $2) AND (b < 4))
- -> Parallel Seq Scan on ab_a2_b2 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b2 (actual rows=0 loops=N)
Filter: ((a >= $1) AND (a <= $2) AND (b < 4))
- -> Parallel Seq Scan on ab_a2_b3 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b3 (actual rows=0 loops=N)
Filter: ((a >= $1) AND (a <= $2) AND (b < 4))
(13 rows)
@@ -1843,59 +1861,59 @@ execute ab_q5 (1, 2, 3);
(1 row)
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (1, 1, 1);
- QUERY PLAN
+select explain_parallel_append('ab_q5', '{1, 1, 1}');
+ explain_parallel_append
-------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=3 loops=1)
Workers Planned: 2
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Parallel Append (actual rows=0 loops=1)
+ Workers Launched: 2
+ -> Partial Aggregate (actual rows=1 loops=3)
+ -> Parallel Append (actual rows=0 loops=N)
Subplans Removed: 6
- -> Parallel Seq Scan on ab_a1_b1 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a1_b1 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a1_b2 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a1_b2 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a1_b3 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a1_b3 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
(13 rows)
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (2, 3, 3);
- QUERY PLAN
+select explain_parallel_append('ab_q5', '{2, 3, 3}');
+ explain_parallel_append
-------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=3 loops=1)
Workers Planned: 2
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Parallel Append (actual rows=0 loops=1)
+ Workers Launched: 2
+ -> Partial Aggregate (actual rows=1 loops=3)
+ -> Parallel Append (actual rows=0 loops=N)
Subplans Removed: 3
- -> Parallel Seq Scan on ab_a2_b1 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b1 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a2_b2 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b2 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a2_b3 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a2_b3 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a3_b1 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a3_b1 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a3_b2 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a3_b2 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
- -> Parallel Seq Scan on ab_a3_b3 (actual rows=0 loops=1)
+ -> Parallel Seq Scan on ab_a3_b3 (actual rows=0 loops=N)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
(19 rows)
-- Try some params whose values do not belong to any partition.
-- We'll still get a single subplan in this case, but it should not be scanned.
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (33, 44,
55);
- QUERY PLAN
+select explain_parallel_append('ab_q5', '{33, 44, 55}');
+ explain_parallel_append
-------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=3 loops=1)
Workers Planned: 2
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Parallel Append (actual rows=0 loops=1)
+ Workers Launched: 2
+ -> Partial Aggregate (actual rows=1 loops=3)
+ -> Parallel Append (actual rows=0 loops=N)
Subplans Removed: 8
-> Parallel Seq Scan on ab_a1_b1 (never executed)
Filter: ((b < 4) AND (a = ANY (ARRAY[$1, $2, $3])))
@@ -1951,16 +1969,16 @@ execute ab_q6 (1, 2, 3);
(1 row)
-explain (analyze, costs off, summary off, timing off) execute ab_q6 (0, 0, 1);
- QUERY PLAN
+select explain_parallel_append('ab_q6', '{0, 0, 1}');
+ explain_parallel_append
---------------------------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=2 loops=1)
Workers Planned: 1
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Nested Loop (actual rows=0 loops=1)
- -> Parallel Seq Scan on lprt_a a (actual rows=102
loops=1)
+ Workers Launched: 1
+ -> Partial Aggregate (actual rows=1 loops=2)
+ -> Nested Loop (actual rows=0 loops=2)
+ -> Parallel Seq Scan on lprt_a a (actual rows=51 loops=N)
Filter: (a = ANY ('{0,0,1}'::integer[]))
-> Append (actual rows=0 loops=102)
-> Index Scan using ab_a1_b1_a_idx on ab_a1_b1
(actual rows=0 loops=2)
@@ -1988,12 +2006,12 @@ explain (analyze, costs off, summary off, timing off)
execute ab_q6 (1, 0, 3);
QUERY PLAN
---------------------------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=2 loops=1)
Workers Planned: 1
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Nested Loop (actual rows=0 loops=1)
- -> Parallel Seq Scan on lprt_a a (actual rows=104
loops=1)
+ Workers Launched: 1
+ -> Partial Aggregate (actual rows=1 loops=2)
+ -> Nested Loop (actual rows=0 loops=2)
+ -> Parallel Seq Scan on lprt_a a (actual rows=52 loops=2)
Filter: (a = ANY ('{1,0,3}'::integer[]))
-> Append (actual rows=0 loops=104)
-> Index Scan using ab_a1_b1_a_idx on ab_a1_b1
(actual rows=0 loops=2)
@@ -2020,14 +2038,14 @@ explain (analyze, costs off, summary off, timing off)
execute ab_q6 (1, 0, 0);
QUERY PLAN
---------------------------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=2 loops=1)
Workers Planned: 1
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Nested Loop (actual rows=0 loops=1)
- -> Parallel Seq Scan on lprt_a a (actual rows=102
loops=1)
+ Workers Launched: 1
+ -> Partial Aggregate (actual rows=1 loops=2)
+ -> Nested Loop (actual rows=0 loops=2)
+ -> Parallel Seq Scan on lprt_a a (actual rows=51 loops=2)
Filter: (a = ANY ('{1,0,0}'::integer[]))
- Rows Removed by Filter: 2
+ Rows Removed by Filter: 1
-> Append (actual rows=0 loops=102)
-> Index Scan using ab_a1_b1_a_idx on ab_a1_b1
(actual rows=0 loops=2)
Index Cond: (a = a.a)
@@ -2054,14 +2072,14 @@ explain (analyze, costs off, summary off, timing off)
execute ab_q6 (1, 0, 0);
QUERY PLAN
--------------------------------------------------------------------------------------------
Finalize Aggregate (actual rows=1 loops=1)
- -> Gather (actual rows=1 loops=1)
+ -> Gather (actual rows=2 loops=1)
Workers Planned: 1
- Workers Launched: 0
- -> Partial Aggregate (actual rows=1 loops=1)
- -> Nested Loop (actual rows=0 loops=1)
- -> Parallel Seq Scan on lprt_a a (actual rows=100
loops=1)
+ Workers Launched: 1
+ -> Partial Aggregate (actual rows=1 loops=2)
+ -> Nested Loop (actual rows=0 loops=2)
+ -> Parallel Seq Scan on lprt_a a (actual rows=50 loops=2)
Filter: (a = ANY ('{1,0,0}'::integer[]))
- Rows Removed by Filter: 2
+ Rows Removed by Filter: 1
-> Append (actual rows=0 loops=100)
-> Index Scan using ab_a1_b1_a_idx on ab_a1_b1
(never executed)
Index Cond: (a = a.a)
diff --git a/src/test/regress/sql/partition_prune.sql
b/src/test/regress/sql/partition_prune.sql
index 3ba4669ad5..6677d460aa 100644
--- a/src/test/regress/sql/partition_prune.sql
+++ b/src/test/regress/sql/partition_prune.sql
@@ -360,6 +360,29 @@ execute ab_q3 (1, 8);
explain (analyze, costs off, summary off, timing off) execute ab_q3 (2, 2);
-- Parallel append
+
+-- Suppress the number of loops each parallel node runs for. This is because
+-- more than one worker may run the same parallel node if timing conditions
+-- are just right, which destabilizes the test.
+create function explain_parallel_append(text, int[]) returns setof text
+language plpgsql as
+$$
+declare
+ ln text;
+ args text := string_agg(u::text, ', ') from unnest($2) u;
+begin
+ for ln in
+ execute format('explain (analyze, costs off, summary off, timing off)
execute %s(%s)',
+ $1, args)
+ loop
+ if ln like '%Parallel%' then
+ ln := regexp_replace(ln, 'loops=\d*', 'loops=N');
+ end if;
+ return next ln;
+ end loop;
+end;
+$$;
+
prepare ab_q4 (int, int) as
select avg(a) from ab where a between $1 and $2 and b < 4;
@@ -367,13 +390,8 @@ select avg(a) from ab where a between $1 and $2 and b < 4;
set parallel_setup_cost = 0;
set parallel_tuple_cost = 0;
set min_parallel_table_scan_size = 0;
-
--- set this so we get a parallel plan
set max_parallel_workers_per_gather = 2;
--- and zero this so that workers don't destabilize the explain output
-set max_parallel_workers = 0;
-
-- Execute query 5 times to allow choose_custom_plan
-- to start considering a generic plan.
execute ab_q4 (1, 8);
@@ -381,8 +399,7 @@ execute ab_q4 (1, 8);
execute ab_q4 (1, 8);
execute ab_q4 (1, 8);
execute ab_q4 (1, 8);
-
-explain (analyze, costs off, summary off, timing off) execute ab_q4 (2, 2);
+select explain_parallel_append('ab_q4', '{2, 2}');
-- Test run-time pruning with IN lists.
prepare ab_q5 (int, int, int) as
@@ -396,12 +413,12 @@ execute ab_q5 (1, 2, 3);
execute ab_q5 (1, 2, 3);
execute ab_q5 (1, 2, 3);
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (1, 1, 1);
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (2, 3, 3);
+select explain_parallel_append('ab_q5', '{1, 1, 1}');
+select explain_parallel_append('ab_q5', '{2, 3, 3}');
-- Try some params whose values do not belong to any partition.
-- We'll still get a single subplan in this case, but it should not be scanned.
-explain (analyze, costs off, summary off, timing off) execute ab_q5 (33, 44,
55);
+select explain_parallel_append('ab_q5', '{33, 44, 55}');
-- Test parallel Append with IN list and parameterized nested loops
create table lprt_a (a int not null);
@@ -434,7 +451,7 @@ execute ab_q6 (1, 2, 3);
execute ab_q6 (1, 2, 3);
execute ab_q6 (1, 2, 3);
-explain (analyze, costs off, summary off, timing off) execute ab_q6 (0, 0, 1);
+select explain_parallel_append('ab_q6', '{0, 0, 1}');
insert into lprt_a values(3),(3);
