Re: Choosing parallel_degree

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.

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.

Let's leave out the parallel_threshold stuff for now.

--
Robert Haas
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