Re: Parallel Inserts in CREATE TABLE AS

On Thu, Dec 24, 2020 at 10:25 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
>
> On Tue, Dec 22, 2020 at 2:16 PM Bharath Rupireddy
> <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> >
> > On Tue, Dec 22, 2020 at 12:32 PM Bharath Rupireddy
> > Attaching v14 patch set that has above changes. Please consider this
> > for further review.
> >
>
> Few comments:
> In the below case, should create be above Gather?
> postgres=# explain create table t7 as select * from t6;
> QUERY PLAN
> -------------------------------------------------------------------
> Gather (cost=0.00..9.17 rows=0 width=4)
> Workers Planned: 2
> -> Create t7
> -> Parallel Seq Scan on t6 (cost=0.00..9.17 rows=417 width=4)
> (4 rows)
>
> Can we change it to something like:
> -------------------------------------------------------------------
> Create t7
> -> Gather (cost=0.00..9.17 rows=0 width=4)
> Workers Planned: 2
> -> Parallel Seq Scan on t6 (cost=0.00..9.17 rows=417 width=4)
> (4 rows)
>

I think it is better to have it in a way as in the current patch
because that reflects that we are performing insert/create below
Gather which is the purpose of this patch. I think this is similar to
what the Parallel Insert patch [1] has for a similar plan.

[1] - https://commitfest.postgresql.org/31/2844/

--
With Regards,
Amit Kapila.