Horton

Re: BUG #15324: Non-deterministic behaviour from parallelised sub-query

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Marko Tiikkaja <marko@joh.to>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Andrew Fletcher <andy@prestigedigital.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2018-08-14T11:50:17Z
Lists: pgsql-bugs

Commits

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  1. Don't allow LIMIT/OFFSET clause within sub-selects to be pushed to workers.

  2. Back-patch "Fix parallel hash join path search."

  3. Prohibit pushing subqueries containing window function calculation to

  4. Fix parallel hash join path search.

On Tue, Aug 14, 2018 at 4:42 PM, Marko Tiikkaja <marko@joh.to> wrote:
> Hi Amit,
>
>> >
>> > This seems broken as well:
>> >
>> >     create table qwr(a int not null, b int not null, c text not null);
>> >     insert into qwr select i, i, (select prosrc from pg_proc where
>> > oid=11734) from generate_series(1, 128000) i;
>> >     set parallel_setup_cost to 0;
>> >     analyze qwr;
>> >     select count(*) from qwr where (a, b) in (select a, row_number()
>> > over()
>> > from qwr);
>> >
>>
>> I am getting below error in above steps:
>>
>> postgres=#     insert into qwr select i, i, (select prosrc from
>> pg_proc where oid=11734) from generate_series(1, 128000) i;
>> ERROR:  null value in column "c" violates not-null constraint
>> DETAIL:  Failing row contains (1, 1, null).
>
>
> Sorry, try this instead:
>
>  insert into qwr select i, i, (select prosrc from pg_proc where
> oid='ts_debug(regconfig,text)'::regprocedure) from generate_series(1,
> 128000) i;
>

This looks related, but I think this is a different issue.  The real
reason for this case is that row_number is marked as parallel_safe
which seems to be wrong.  I think it should be marked as
parallel_unsafe.   This needs some more analysis w.r.t which other
Window functions has a similar problem.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com