| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Josh berkus <josh(at)agliodbs(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>, Amit Kapila <amit(dot)kapila16(at)gmail(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: | 2016-06-01 02:11:01 |
| Message-ID: | CA+TgmoaHSOQbk1Z7vRdrW+Ujg35AsuZnEm2Yn_6pWA1UPqL1Ww@mail.gmail.com |
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On Tue, May 31, 2016 at 10:02 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Now, this case is a little trickier. If we called it simply
>> parallel_degree rather than max_parallel_degree, then it would have
>> the same name as the reloption. But the reloption sets an exact
>> value, and the GUC sets a cap, which is a significant difference.
>
> The reloption does not set an exact value, according to the code:
>
> /*
> * Use the table parallel_degree, but don't go further than
> * max_parallel_degree.
> */
> parallel_degree = Min(rel->rel_parallel_degree, max_parallel_degree);
>
> although the existing documentation for it is so vague that you
> couldn't tell from that.
True, max_parallel_degree is an overriding limit. But the point is
that, without the reloption, you can't get lots of workers on a small
table. The reloption lets you do that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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