Re: Parallelize correlated subqueries that execute within each worker

On Mon, Mar 21, 2022 at 8:48 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2022-01-22 20:25:19 -0500, James Coleman wrote:
> > On the other hand this is a dramatically simpler patch series.
> > Assuming the approach is sound, it should much easier to maintain than
> > the previous version.
> >
> > The final patch in the series is a set of additional checks I could
> > imagine to try to be more explicit, but at least in the current test
> > suite there isn't anything at all they affect.
> >
> > Does this look at least somewhat more like what you'd envisionsed
> > (granting the need to squint hard given the relids checks instead of
> > directly checking params)?
>
> This fails on freebsd (so likely a timing issue): https://cirrus-ci.com/task/4758411492458496?logs=test_world#L2225
>
> Marked as waiting on author.

I've finally gotten around to checking this out, and the issue was an
"explain analyze" test that had actual loops different on FreeBSD.
There doesn't seem to be a way to disable loop output, but instead of
processing the explain output with e.g. a function (as we do some
other places) to remove the offending and unnecessary output I've just
removed the "analyze" (as I don't believe it was actually necessary).

Attached is an updated patch series. In this version I've removed the
"parallelize some subqueries with limit" patch since discussion is
proceeding in the spun off thread. The first patch adds additional
tests so that you can see how those new tests change with the code
changes in the 2nd patch in the series. As before the final patch in
the series includes changes where we may also want to verify
correctness but don't have a test demonstrating the need.

Thanks,
James Coleman