Re: Parallel Seq Scan

2015-11-11 16:18 GMT+01:00 Thom Brown <thom(at)linux(dot)com>:

> On 11 November 2015 at 14:53, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > On Mon, Nov 9, 2015 at 11:15 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> >> Okay, I have updated the patch to make seq scan node parallel aware.
> >> To make that happen we need to have parallel_aware flag both in Plan
> >> as well as Path, so that we can pass that information from Path to Plan.
> >> I think the right place to copy parallel_aware info from path to
> >> plan is copy_path_costsize and ideally we should change the name
> >> of function to something like copy_generic_path_info(), but for
> >> now I have retained it's original name as it is used at many places,
> >> let me know if you think we should goahead and change the name
> >> of function as well.
> >>
> >> I have changed Explain as well so that it adds Parallel for Seq Scan if
> >> SeqScan node is parallel_aware.
> >>
> >> I have not integrated it with consider-parallel patch, so that this and
> >> Partial Seq Scan version of the patch can be compared without much
> >> difficulity.
> >>
> >> Thoughts?
> >
> > I've committed most of this, except for some planner bits that I
> > didn't like, and after a bunch of cleanup. Instead, I committed the
> > consider-parallel-v2.patch with some additional planner bits to make
> > up for the ones I removed from your patch. So, now we have parallel
> > sequential scan!
> >
> > For those following along at home, here's a demo:
> >
> > rhaas=# \timing
> > Timing is on.
> > rhaas=# select * from pgbench_accounts where filler like '%a%';
> > aid | bid | abalance | filler
> > -----+-----+----------+--------
> > (0 rows)
> >
> > Time: 743.061 ms
> > rhaas=# set max_parallel_degree = 4;
> > SET
> > Time: 0.270 ms
> > rhaas=# select * from pgbench_accounts where filler like '%a%';
> > aid | bid | abalance | filler
> > -----+-----+----------+--------
> > (0 rows)
> >
> > Time: 213.412 ms
> >
> > This is all pretty primitive at this point - there are still lots of
> > things that need to be fixed and improved, and it applies to only the
> > very simplest cases at present, but, hey, parallel query. Check it
> > out.
>
> Congratulations to both you and Amit. This is a significant landmark
> in PostgreSQL feature development.
>

+1

Pavel

>
> Thom
>
>
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