Horton

Re: strange parallel query behavior after OOM crashes

Kuntal Ghosh <kuntalghosh.2007@gmail.com>

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From: Kuntal Ghosh <kuntalghosh.2007@gmail.com>
To: Neha Khatri <nehakhatri5@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-04-05T07:34:16Z
Lists: pgsql-hackers 
On Tue, Apr 4, 2017 at 12:16 PM, Neha Khatri <nehakhatri5@gmail.com> wrote:

> I feel there should be an assert if
>     (BackgroundWorkerData->parallel_register_count -
> BackgroundWorkerData->parallel_terminate_count) > max_parallel_workers)
>
Backend 1 > SET max_parallel_worker = 8;
Backend 1 > Execute a long running parallel query q1 with number of
parallel worker spawned is say, 4.
Backend 2> SET max_parallel_worker = 3;
Backend 2 > Execute a long running parallel query q2 with number of
parallel worker spawned > 0.

The above assert statement will bring down the server unnecessarily
while executing q2.

-- 
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. Add an Assert() to max_parallel_workers enforcement.

  2. Fix confusion of max_parallel_workers mechanism following crash.

  3. Add max_parallel_workers GUC.