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: Robert Haas <robertmhaas@gmail.com>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-04-03T10:08:56Z
Lists: pgsql-hackers

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On Fri, Mar 31, 2017 at 6:50 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Mar 30, 2017 at 4:35 PM, Kuntal Ghosh
> <kuntalghosh.2007@gmail.com> wrote:
>> 2. the server restarts automatically, initialize
>> BackgroundWorkerData->parallel_register_count and
>> BackgroundWorkerData->parallel_terminate_count in the shared memory.
>> After that, it calls ForgetBackgroundWorker and it increments
>> parallel_terminate_count.
>
> Hmm.  So this seems like the root of the problem.  Presumably those
> things need to be reset AFTER forgetting any background workers from
> before the crash.
>
IMHO, the fix would be not to increase the terminated parallel worker
count whenever ForgetBackgroundWorker is called due to a bgworker
crash. I've attached a patch for the same. PFA.



-- 
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.