Re: Result Cache node shows per-worker info even for workers not launched

From: Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>
To: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Cc: David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Result Cache node shows per-worker info even for workers not launched
Date: 2021-04-28 10:41:58
Message-ID: CAJ3gD9d_ZqercSJQKF6rKz+5huxUBhrYFsXNxyZ5158GY7F+5w@mail.gmail.com
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On Wed, 28 Apr 2021 at 15:08, Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> On Wed, Apr 28, 2021 at 1:54 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> > I plan to push this in the next 24 hours or so.
>
> I happen to see explain_resultcache in resultcache.sql, seems like two
> of the tests still have numbers for cache hits and misses - Hits: 980
> Misses: 20, won't these make tests unstable? Will these numbers be
> same across machines? Or is it that no buildfarm had caught these? The
> comment below says that, the hits and misses are not same across
> machines:
> -- Ensure we get some evictions. We're unable to validate the hits and misses
> -- here as the number of entries that fit in the cache at once will vary
> -- between different machines.
>
> Should we remove the hide_hitmiss parameter in explain_resultcache and
> always print N for non-zero and Zero for 0 hits and misses? This
> clearly shows that we have 0 or non-zero hits or misses.
>
> Am I missing something?

I believe, the assumption here is that with no workers involved, it is
guaranteed to have the exact same cache misses and hits anywhere.

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