Re: Choosing parallel_degree

On 16/03/2016 18:42, Robert Haas wrote:
> On Wed, Mar 16, 2016 at 1:23 PM, Julien Rouhaud
> <julien.rouhaud@dalibo.com> wrote:
>> On 16/03/2016 17:55, Robert Haas wrote:
>>> On Wed, Mar 16, 2016 at 12:47 PM, Julien Rouhaud
>>> <julien.rouhaud@dalibo.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