Horton

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

Marko Tiikkaja <marko@joh.to>

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From: Marko Tiikkaja <marko@joh.to>
To: Amit Kapila <amit.kapila16@gmail.com>
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: 2018-08-14T11:12:56Z
Lists: pgsql-bugs

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  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.

Hi Amit,

On Tue, Aug 14, 2018 at 2:09 PM, Amit Kapila <amit.kapila16@gmail.com>
wrote:

> On Tue, Aug 14, 2018 at 3:52 PM, Marko Tiikkaja <marko@joh.to> wrote:
> > On Tue, Aug 14, 2018 at 7:10 AM, Amit Kapila <amit.kapila16@gmail.com>
> > wrote:
> >>
> >> Yeah, one idea could be that we detect this in
> >> max_parallel_hazard_walker during the very first pass it performs on
> >> query-tree.  Basically, in the SubLink node check, we can detect
> >> whether the subselect has Limit/Offset clause and if so, then we can
> >> treat it as parallel_unsafe.  I have tried that way and it prohibits
> >> the parallel plan for the reported queries.  However, I think more
> >> analysis and verification is required to see if it can happen in any
> >> other related cases.
> >
> >
> > 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;


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