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Allow parallel workers to execute subplans.

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This doesn't do anything to make Param nodes anything other than
parallel-restricted, so this only helps with uncorrelated subplans,
and it's not necessarily very cheap because each worker will run the
subplan separately (just as a Hash Join will build a separate copy of
the hash table in each participating process), but it's a first step
toward supporting cases that are more likely to help in practice, and
is occasionally useful on its own.

Amit Kapila, reviewed and tested by Rafia Sabih, Dilip Kumar, and
me.

Discussion: http://postgr.es/m/CAA4eK1+e8Z45D2n+rnDMDYsVEb5iW7jqaCH_tvPMYau=1Rru9w@mail.gmail.com
This commit is contained in:
Robert Haas
2017-02-14 18:09:47 -05:00
parent 8da9a22636
commit 5e6d8d2bbb
10 changed files with 61 additions and 14 deletions
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9
src/test/regress/sql/select_parallel.sql
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@ -39,6 +39,15 @@ explain (costs off)
select sum(parallel_restricted(unique1)) from tenk1
group by(parallel_restricted(unique1));
-- test parallel plans for queries containing un-correlated subplans.
alter table tenk2 set (parallel_workers = 0);
explain (costs off)
select count(*) from tenk1 where (two, four) not in
(select hundred, thousand from tenk2 where thousand > 100);
select count(*) from tenk1 where (two, four) not in
(select hundred, thousand from tenk2 where thousand > 100);
alter table tenk2 reset (parallel_workers);
set force_parallel_mode=1;
explain (costs off)