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Re: Rename max_parallel_degree?

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Julien Rouhaud <julien.rouhaud@dalibo.com>, Tom Lane <tgl@sss.pgh.pa.us>, Josh Berkus <josh@agliodbs.com>, "David G. Johnston" <david.g.johnston@gmail.com>, Peter Geoghegan <pg@heroku.com>, Noah Misch <noah@leadboat.com>, David Rowley <david.rowley@2ndquadrant.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Magnus Hagander <magnus@hagander.net>, Bruce Momjian <bruce@momjian.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2016-09-17T06:40:24Z
Lists: pgsql-hackers 
On Fri, Sep 16, 2016 at 11:54 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>
> +       /*
> +        * We need a write barrier to make sure the update of
> +        * parallel_terminate_count is done before the store to in_use
> +        */
>
> Does the order actually matter here?
>

I think so.  If slot->in_use is reordered before the check of
is_parallel_worker, then it is possible that concurrent registration
of worker can mark the is_parallel_worker as false before we check the
flag here.  See explanation in previous e-mail [1].


[1] - https://www.postgresql.org/message-id/CAA4eK1%2BQ_DdJ28qXYSHZiBKNf2MY1QFrv5XAOAw4ZXHw4TPMxA%40mail.gmail.com

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