Re: Rename max_parallel_degree?

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Josh berkus <josh@agliodbs.com>, Peter Geoghegan <pg@heroku.com>, Noah Misch <noah@leadboat.com>, David Rowley <david.rowley@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Magnus Hagander <magnus@hagander.net>, Bruce Momjian <bruce@momjian.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2016-06-01T02:11:01Z

Lists: pgsql-hackers

On Tue, May 31, 2016 at 10:02 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.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