From: | Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, James Sewell <james(dot)sewell(at)lisasoft(dot)com> |
Subject: | Re: Choosing parallel_degree |
Date: | 2016-03-16 18:05:50 |
Message-ID: | 56E9A07E.60206@dalibo.com |
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Thread: | |
Lists: | pgsql-hackers |
On 16/03/2016 18:42, Robert Haas wrote:
> On Wed, Mar 16, 2016 at 1:23 PM, Julien Rouhaud
> <julien(dot)rouhaud(at)dalibo(dot)com> wrote:
>> On 16/03/2016 17:55, Robert Haas wrote:
>>> On Wed, Mar 16, 2016 at 12:47 PM, Julien Rouhaud
>>> <julien(dot)rouhaud(at)dalibo(dot)com> wrote:
>>>> Something like a "min_parallel_degree" then ?
>>>
>>> Why not just parallel_degree without any prefix? As in, when scanning
>>> this table in parallel, the reloption suggests using N workers.
>>>
>>
>> Agreed.
>>
>> PFA v2 that implements that.
>
> I think create_parallel_paths shouldn't actually run the loop if the
> reloption is specified; it should just adopt the specified value (or
> max_parallel_degree, whichever is less). Right now, you have it doing
> the work to compute the default value but then overriding it.
>
Oh ugly mistake. Fixed.
> Also, I think parallel_degree should be down in the section that says
> /* information about a base rel (not set for join rels!) */ and I
> think it should be called something like rel_parallel_degree, to make
> it more clear that it's a value set on the relation level.
>
You're right, fixed.
> Let's leave out the parallel_threshold stuff for now.
>
attached v3 drops the GUC part.
--
Julien Rouhaud
http://dalibo.com - http://dalibo.org
Attachment | Content-Type | Size |
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rel_parallel_degree_v3.diff | text/x-patch | 6.4 KB |
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