Subject: max_worker_processes default not documented

From: "David G. Johnston" <[email-masked]>
Date: Sat, 7 May 2016 20:16:37 -0700

While this may be in the postgresql.conf it's absence in the docs is made
noticeable by the fact both the immediately preceding and subsequent items
in the 9.6 docs specify their default values.  Furthermore,
max_parallel_degree defaults to 2 but the workers come from the pool sized
using max_worker_processes - provoking the very question as to how many is
2 relative to the default pool size.

http://www.postgresql.org/docs/devel/static/runtime-config-resource.html#GUC-MAX-PARALLEL-DEGREE

David J.

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From: Peter Eisentraut <[email-masked]>
Date: Thu, 12 May 2016 09:20:28 -0400

> 2 relative to the default pool size.

done

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Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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From: "David G. Johnston" <[email-masked]>
Date: Thu, 12 May 2016 06:24:36 -0700

On Thursday, May 12, 2016, Peter Eisentraut <
[email-masked]

>> 2 relative to the default pool size.
 Thanks.  Now for a related question.  Are any of those workers permanently
in use?  And what processes use them.  I can think of checkpoint writer and
autovacuum off the top of my head that are potential candidates.

David J.

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From: Peter Eisentraut <[email-masked]>
Date: Tue, 2 Aug 2016 13:57:15 -0400

On 5/12/16 9:24 AM, David G. Johnston wrote:
>  Thanks.  Now for a related question.  Are any of those workers
> permanently in use?  And what processes use them.  I can think of
> checkpoint writer and autovacuum off the top of my head that are
> potential candidates.

max_worker_processes only controls "background workers".  The other
facilities you mention don't count as such (confusingly perhaps).

Before 9.6, the only background workers were from extensions.  In 9.6,
the parallel workers also use the background worker facilities and count
against max_worker_processes.

More documentation is possible here.  I think maybe a section somewhere
that summarizes all the parallel-related settings.  And also something
in the release notes noting that max_worker_processes is now also used
by built-in facilities, so you should increase it if you have previously
adjusted it for something.