| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Josh Berkus <josh(at)agliodbs(dot)com>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Rename max_parallel_degree? |
| Date: | 2016-09-19 18:19:26 |
| Message-ID: | CA+TgmoZS7DFFGz7kKWLoTAsNnXRKUiQFDt5yHgf4L73z52dgAQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Sep 17, 2016 at 2:40 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Fri, Sep 16, 2016 at 11:54 PM, Robert Haas <robertmhaas(at)gmail(dot)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
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