Re: Parallel Seq Scan

On Fri, Nov 6, 2015 at 10:13 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Nov 5, 2015 at 10:49 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> > On Thu, Nov 5, 2015 at 11:54 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
wrote:
> >> I was thinking about this idea:
> >>
> >> 1. Add a parallel_aware flag to each plan.
> >
> > Okay, so shall we add it in generic Plan node or to specific plan nodes
> > like SeqScan, IndexScan, etc. To me, it appears that parallelism is
> > a node specific property, so we should add it to specific nodes and
> > for now as we are parallelising seq scan, so we can add this flag in
> > SeqScan node. What do you say?
>
> I think it should go in the Plan node itself. Parallel Append is
> going to need a way to test whether a node is parallel-aware, and
> there's nothing simpler than if (plan->parallel_aware). That makes
> life simple for EXPLAIN, too.
>

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?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com