Re: Sequential parallel scan / agg - Mailing list pgsql-general
OK, looks like this question is answered by the wiki:
Even when parallel query is enabled in general, the query planner will never generate a parallel plan if any of the following are true:
- The query writes data. If a query contains a data-modifying operation either at the top level or within a CTE, no parallel plans for that query will be generated. This is a limitation of the current implementation which could be lifted in a future release.
Sad, but looks to hold from this testing!
James Sewell,
PostgreSQL Team Lead / Solutions Architect
Suite 112, Jones Bay Wharf, 26-32 Pirrama Road, Pyrmont NSW 2009
On Mon, Nov 14, 2016 at 11:13 AM, James Sewell <james.sewell@jirotech.com> wrote:
Hi,Yes, same result (non-parallel seq scan)Cheers,James Sewell,PostgreSQL Team Lead / Solutions ArchitectSuite 112, Jones Bay Wharf, 26-32 Pirrama Road, Pyrmont NSW 2009On Mon, Nov 14, 2016 at 10:43 AM, melvin6925 <melvin6925@gmail.com> wrote:Have you tried:CREATE TABLE blah AS SELECT ... ?Sent via the Samsung Galaxy S® 6, an AT&T 4G LTE smartphone-------- Original message --------From: James Sewell <james.sewell@jirotech.com>Date: 11/13/16 18:04 (GMT-05:00)To: pgsql-general <pgsql-general@postgresql.org>Subject: [GENERAL] Sequential parallel scan / aggHi 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=# explaininsert into jirotech.test(select count(*) FROM meter_read mrwhere 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=# explainwith a as(select count(*) FROM meter_read mrwhere 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=# explainselect count(*) into jirotech.jamestest FROM meter_read mrwhere 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 mstest=# explainselect count(*) FROM meter_read mrwhere 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 msCheers,James Sewell,PostgreSQL Team Lead / Solutions ArchitectSuite 112, Jones Bay Wharf, 26-32 Pirrama Road, Pyrmont NSW 2009
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