Re: Append with naive multiplexing of FDWs

On Fri, Dec 6, 2019 at 9:20 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Dec 5, 2019 at 1:12 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > I agree with Stephen's request. We have been waiting for the executor
> > rewrite for a while, so let's just do something simple and see how it
> > performs.
>
> I'm sympathetic to the frustration here, and I think it would be great
> if we could find a way forward that doesn't involve waiting for a full
> rewrite of the executor. However, I seem to remember that when we
> tested the various patches that various people had written for this
> feature (I wrote one, too) they all had a noticeable performance
> penalty in the case of a plain old Append that involved no FDWs and
> nothing asynchronous. I don't think it's OK to have, say, a 2%
> regression on every query that involves an Append, because especially
> now that we have partitioning, that's a lot of queries.
>
> I don't know whether this patch has that kind of problem. If it
> doesn't, I would consider that a promising sign.

I'll look into that. If there is a measurable impact, I suspect it
can be avoided by, for example, installing a different ExecProcNode
function.