Re: Parallel Seq Scan

José,

* José Luis Tallón (jltallon@adv-solutions.net) wrote:
> On 12/04/2014 07:35 AM, Amit Kapila wrote:
> >The number of worker backends that can be used for
> >parallel seq scan can be configured by using a new GUC
> >parallel_seqscan_degree, the default value of which is zero
> >and it means parallel seq scan will not be considered unless
> >user configures this value.
>
> The number of parallel workers should be capped (of course!) at the
> maximum amount of "processors" (cores/vCores, threads/hyperthreads)
> available.
>
> More over, when load goes up, the relative cost of parallel working
> should go up as well.
> Something like:
>     p = number of cores
>     l = 1min-load
>
>     additional_cost = tuple estimate * cpu_tuple_cost * (l+1)/(c-1)
>
> (for c>1, of course)

While I agree in general that we'll need to come up with appropriate
acceptance criteria, etc, I don't think we want to complicate this patch
with that initially.  A SUSET GUC which caps the parallel GUC would be
enough for an initial implementation, imv.

> Not directly (I haven't had the time to read the code yet), but I'm
> thinking about the ability to simply *replace* executor methods from
> an extension.

You probably want to look at the CustomScan thread+patch directly then..
Thanks,
    Stephen