On Wed, Dec 16, 2015 at 6:04 PM, Robert Haas <robertmh...@gmail.com> wrote:
> On Wed, Dec 16, 2015 at 1:34 AM, Amit Kapila <amit.kapil...@gmail.com>
> > Yes, thats one thing I wanted to know, yet another point which is not
> > clear to me about this Async infrastructure is why the current
> > infrastructure
> > of Parallelism can't be used to achieve the Async benefits of
> Well, all a ForeignScan by postgres_fdw does is read the tuples that
> are generated remotely.  Turning around and sticking those into a
> Funnel doesn't seem like it gains much: now instead of having to read
> tuples from someplace, the leader has to read tuples from some other
> place.  Yeah, there are cases where it could win, like when there's a
> selective nonpushable qual, but that's not that exciting.
> There's another, more serious problem: if the leader has a connection
> open to the remote server and that connection is in mid-transaction,
> you can't have a worker open a new connection without changing the
> semantics.  Working around that problem looks hard to me.

Okay.  It seems there are cases where it could benefit from Async
execution infrastructure instead of directly using Gather node kind
of infrastructure.  I am not the right person to judge whether there
are enough cases that we need a new infrastructure for such executions,
but I think it is a point to consider and I am sure you will make the
right move.

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

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