Sequential parallel scan / agg - Mailing list pgsql-general
Hi all,
I have a customer who is making use of the new parallel features on a 64 core box - this is working really well for them. However one issue (which I've since realised I've never seen an example of) is getting the data from these queries into a table.
I can't seem to create a plan which does this and still uses multiple workers, probably best to just show by example.
Below you can see:
- INSERT ... SELECT doesn't work
- WITH a AS (SELECT ...) INSERT FROM a doesn't work
- SELECT .. INTO doesn't work
- SELECT with no insert does work as expected
test=# explain
insert into jirotech.test
(select count(*) FROM meter_read mr
where TIMESTAMP_ROUNDED >= (timestamp'2016-03-30 00:00:00' - interval '2' day)
and TIMESTAMP_ROUNDED < timestamp'2016-03-30 00:00:00' )
;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Insert on test (cost=13336866.41..13336866.44 rows=1 width=438)
-> Subquery Scan on "*SELECT*" (cost=13336866.41..13336866.44 rows=1 width=438)
-> Aggregate (cost=13336866.41..13336866.42 rows=1 width=8)
-> Append (cost=0.00..12405302.12 rows=372625715 width=0)
-> Seq Scan on meter_read mr (cost=0.00..0.00 rows=1 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_29 mr_1 (cost=0.00..6201295.24 rows=186240748 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_28 mr_2 (cost=0.00..6204006.88 rows=186384966 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
(10 rows)
test=# explain
with a as
(select count(*) FROM meter_read mr
where TIMESTAMP_ROUNDED >= (timestamp'2016-03-30 00:00:00' - interval '2' day)
and TIMESTAMP_ROUNDED < timestamp'2016-03-30 00:00:00' )
INSERT INTO jirotech.test SELECT * FROM A
;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Insert on test (cost=13336866.42..13336866.45 rows=1 width=438)
CTE a
-> Aggregate (cost=13336866.41..13336866.42 rows=1 width=8)
-> Append (cost=0.00..12405302.12 rows=372625715 width=0)
-> Seq Scan on meter_read mr (cost=0.00..0.00 rows=1 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_29 mr_1 (cost=0.00..6201295.24 rows=186240748 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_28 mr_2 (cost=0.00..6204006.88 rows=186384966 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> CTE Scan on a (cost=0.00..0.03 rows=1 width=438)
(11 rows)
test=# explain
select count(*) into jirotech.jamestest FROM meter_read mr
where TIMESTAMP_ROUNDED >= (timestamp'2016-03-30 00:00:00' - interval '2' day)
and TIMESTAMP_ROUNDED < timestamp'2016-03-30 00:00:00'
;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=13336866.41..13336866.42 rows=1 width=8)
-> Append (cost=0.00..12405302.12 rows=372625715 width=0)
-> Seq Scan on meter_read mr (cost=0.00..0.00 rows=1 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_29 mr_1 (cost=0.00..6201295.24 rows=186240748 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Seq Scan on meter_read_2016_03_28 mr_2 (cost=0.00..6204006.88 rows=186384966 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
(8 rows)
Time: 29.229 ms
test=# explain
select count(*) FROM meter_read mr
where TIMESTAMP_ROUNDED >= (timestamp'2016-03-30 00:00:00' - interval '2' day)
and TIMESTAMP_ROUNDED < timestamp'2016-03-30 00:00:00'
;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Finalize Aggregate (cost=7631566.71..7631566.72 rows=1 width=8)
-> Gather (cost=7631566.68..7631566.69 rows=8 width=8)
Workers Planned: 8
-> Partial Aggregate (cost=7630566.68..7630566.69 rows=1 width=8)
-> Append (cost=0.00..7514121.14 rows=46578216 width=0)
-> Parallel Seq Scan on meter_read mr (cost=0.00..0.00 rows=1 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Parallel Seq Scan on meter_read_2016_03_29 mr_1 (cost=0.00..3756417.28 rows=23280094 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
-> Parallel Seq Scan on meter_read_2016_03_28 mr_2 (cost=0.00..3757703.86 rows=23298121 width=0)
Filter: ((timestamp_rounded >= '2016-03-28 00:00:00'::timestamp without time zone) AND (timestamp_rounded < '2016-03-30 00:00:00'::timestamp without time zone))
(11 rows)
Time: 29.819 ms
Cheers,
James Sewell,
PostgreSQL Team Lead / Solutions Architect
Suite 112, Jones Bay Wharf, 26-32 Pirrama Road, Pyrmont NSW 2009
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