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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Josh berkus <josh@agliodbs.com>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Peter Geoghegan <pg@heroku.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Noah Misch <noah@leadboat.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Rename max_parallel_degree?
Date: Tue, 31 May 2016 14:29:56 -0400
Message-ID: <22406.1464719396@sss.pgh.pa.us> (raw)
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Josh berkus <josh@agliodbs.com> writes:
> One more consistency question: what's the effect of running out of
> max_parallel_workers?

ITYM max_worker_processes (ie, the cluster-wide pool size)?

> That is, say max_parallel_workers is set to 10, and 8 are already
> allocated.  If I ask for max_parallel_X = 4, how many cores to I use?

One of my reasons for liking max_parallel_workers is that you can sensibly
compare it to max_worker_processes to figure out how many workers you're
likely to get.  If you think in terms of "degree" it takes some additional
mental arithmetic to understand what will happen.

> Presumably the leader isn't counted towards max_parallel_workers?

Not under what I'm proposing.

			regards, tom lane


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