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> wrote: > > 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 ForeignScan? > > 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
