Re: Choosing parallel_degree

From: Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com>
To: James Sewell <james(dot)sewell(at)lisasoft(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Paul Ramsey <pramsey(at)cleverelephant(dot)ca>
Subject: Re: Choosing parallel_degree
Date: 2016-04-03 11:07:17
Message-ID: 5700F965.5090303@dalibo.com
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On 22/03/2016 07:58, Julien Rouhaud wrote:
> On 21/03/2016 20:38, Julien Rouhaud wrote:
>> On 21/03/2016 05:18, James Sewell wrote:
>>> OK cool, thanks.
>>>
>>> Can we remove the minimum size limit when the per table degree setting
>>> is applied?
>>>
>>> This would help for tables with 2 - 1000 pages combined with a high CPU
>>> cost aggregate.
>>>
>>
>> Attached v4 implements that. It also makes sure that the chosen
>> parallel_degree won't be more than the relation's estimated number of pages.
>>
>
> And I just realize that it'd prevent from forcing parallelism on
> partitionned table, v5 attached removes the check on the estimated
> number of pages.
>
>

The feature freeze is now very close. If this GUC is still wanted,
should I add this patch to the next commitfest?

--
Julien Rouhaud
http://dalibo.com - http://dalibo.org

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