Re: Parallel INSERT (INTO ... SELECT ...)

On Wed, Sep 30, 2020 at 7:38 AM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
>
> > >
> > > I think you still need to work on the costing part, basically if we
> > > are parallelizing whole insert then plan is like below
> > >
> > > -> Gather
> > > -> Parallel Insert
> > > -> Parallel Seq Scan
> > >
> > > That means the tuple we are selecting via scan are not sent back to
> > > the gather node, so in cost_gather we need to see if it is for the
> > > INSERT then there is no row transferred through the parallel queue
> > > that mean we need not to pay any parallel tuple cost.
> >
> > I just looked into the parallel CTAS[1] patch for the same thing, and
> > I can see in that patch it is being handled.
> >
> > [1] https://www.postgresql.org/message-id/CALj2ACWFq6Z4_jd9RPByURB8-Y8wccQWzLf%2B0-Jg%2BKYT7ZO-Ug%40mail.gmail.com
> >
>
> Hi Dilip,
>
> You're right, the costing for Parallel Insert is not done and
> finished, I'm still working on the costing, and haven't posted an
> updated patch for it yet.

Okay.

> As far as cost_gather() method is concerned, for Parallel INSERT, it
> can probably use the same costing approach as the CTAS patch except in
> the case of a specified RETURNING clause.

Yeah right. I did not think about the returning part.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com