Re: Rename max_parallel_degree?

From: Peter Geoghegan <pg(at)heroku(dot)com>
To: Josh berkus <josh(at)agliodbs(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(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>, 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: 2016-05-31 17:38:26
Message-ID: CAM3SWZS_zL8Wx-zdo_LBJu4ggVqSQZrB_be2Ht1euWQ_AbLerA@mail.gmail.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

On Tue, May 31, 2016 at 10:23 AM, Josh berkus <josh(at)agliodbs(dot)com> wrote:
> It's still WAY simpler to understand "max_parallel is the number of
> parallel workers I requested".

(Sorry Josh, somehow hit reply, not reply-all)

Yes, it is. But as long as parallel workers are not really that
distinct to the leader-as-worker when executing a parallel query, then
you have another consideration. Which is that you need to care about
how many cores your query uses first and foremost, and not the number
of parallel workers used. I don't think that having only one worker
will cause too much confusion, because users will trust that we won't
allow something that simply makes no sense to happen.

In my parallel create index patch, the leader participates as a worker
to scan and sort runs. It's identical to a worker, practically
speaking, at least until time comes to merge those runs. Similarly,
parallel aggregate does not really have much for the leader process to
do other than act as a worker.

--
Peter Geoghegan

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Joshua D. Drake 2016-05-31 17:41:08 Re: Rename max_parallel_degree?
Previous Message Tom Lane 2016-05-31 17:30:36 Re: Rename max_parallel_degree?