Horton
Menu

Re: Rename max_parallel_degree?

Robert Haas <robertmhaas@gmail.com>

View thread
From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@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: 2016-09-19T18:19:26Z
Lists: pgsql-hackers 
On Sat, Sep 17, 2016 at 2:40 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> 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].

Tricky.  I believe you're right.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company