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From: Josh berkus <josh@agliodbs.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
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 10:10:29 -0700
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On 05/31/2016 10:03 AM, Tom Lane wrote:
> Josh berkus <josh@agliodbs.com> writes:
>> I realize there's a lot of water under the bridge here, but I think
>> we're going to get 1000 questions on -general of the type:  "I asked for
>> 8 parallel workers, why did I only get 7?".  I believe we will regret
>> this change.
>> So, one vote from me to revert.
> 
> Well, that gets back to the question of whether average users will
> understand the "degree" terminology.  For the record, while I do not
> like the current behavior either, this was not the solution I favored.
> I thought we should rename the GUC and keep it as meaning the number
> of additional worker processes.

I will happily bet anyone a nice dinner in Ottawa that most users will
not understand it.

Compare this:

"max_parallel is the maximum number of parallel workers which will work
on each stage of the query which is parallizable.  If you set it to 4,
you get up to 4 workers."

with this:

"max_parallel_degree is the amount of parallelism in the query, with the
understanding that the original parent process counts as 1, which means
that if you set it to 1 you get no parallelism, and if you want 4
parallel workers you need to set it to 5."

Which one of those is going to require more explanations on -general and
-novice?  Bets?

Let's not be complicated for the sake of being complicated.

-- 
--
Josh Berkus
Red Hat OSAS
(any opinions are my own)


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