From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@heroku.com>
cc: Josh berkus <josh@agliodbs.com>, Robert Haas <robertmhaas@gmail.com>,
        Noah Misch <noah@leadboat.com>,
        David Rowley <david.rowley@2ndquadrant.com>,
        Amit Kapila <amit.kapila16@gmail.com>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Magnus Hagander <magnus@hagander.net>,
        Bruce Momjian <bruce@momjian.us>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Rename max_parallel_degree?
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Comments: In-reply-to Peter Geoghegan <pg@heroku.com>
	message dated "Tue, 31 May 2016 10:51:28 -0700"
Date: Tue, 31 May 2016 14:08:57 -0400
Message-ID: <21507.1464718137@sss.pgh.pa.us>
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Sender: pgsql-hackers-owner@postgresql.org

Peter Geoghegan <pg@heroku.com> writes:
> Even when the leader is consuming input from workers, that's still perhaps
> pegging one CPU core. So, it doesn't really invalidate what I said about
> the number of cores being the primary consideration.

Agreed, but if we think that people need to be thinking in those terms,
maybe the parameter should be "max_parallel_cores".

The alternate docs patch I just posted tries to deal with this by
describing max_parallel_workers as being the max number of worker
processes used to "assist" a parallel query.  That was terminology
already being used in one place, but not consistently.  If we use it
consistently, I think it would be sufficient to remind people that
they need to figure on one more core for the leader.

			regards, tom lane


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