Re: Duplicate Workers entries in some EXPLAIN plans

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Georgios Kokolatos <gkokolatos(at)pm(dot)me>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Duplicate Workers entries in some EXPLAIN plans
Date: 2020-01-25 19:23:50
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Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com> writes:
> For what it's worth, this version makes sense to me.

Thanks for looking. Here's a version that deals with the JIT
instrumentation. As Andres noted far upthread, that was also
really bogusly done before. Not only could you get multiple "JIT"
subnodes on a Gather node, but we failed to print the info at all
if the parallelism was expressed as Gather Merge rather than

A side effect of this change is that per-worker JIT info is now
printed one plan level further down: before it was printed on
the Gather node, but now it's attached to the Gather's child,
because that's where we print other per-worker data. I don't
see anything particularly wrong with that, but it's another
change from the behavior today.

It's still really unclear to me how we could exercise any of
this behavior meaningfully in a regression test. I thought
for a little bit about using the TAP infrastructure instead
of a traditional-style test, but it seems like that doesn't
buy anything except for a bias towards ignoring details instead
of overspecifying them. Which is not much of an improvement.

regards, tom lane

Attachment Content-Type Size
merge-explain-worker-output-v7.patch text/x-diff 27.5 KB

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