From: Tom Lane <tgl@sss.pgh.pa.us>
To: depesz@depesz.com
cc: PostgreSQL General <pgsql-general@lists.postgresql.org>,
        Andres Freund <andres@anarazel.de>
Subject: Re: Interesting fail when migrating Pg from Ubuntu Bionic to Focal
In-reply-to: <20220306140402.GA6360@depesz.com>
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Comments: In-reply-to hubert depesz lubaczewski <depesz@depesz.com>
	message dated "Sun, 06 Mar 2022 15:04:02 +0100"
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Date: Sun, 06 Mar 2022 11:10:00 -0500
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hubert depesz lubaczewski <depesz@depesz.com> writes:
> On Fri, Mar 04, 2022 at 05:03:14PM -0500, Tom Lane wrote:
>> Mmm ... it might have just been that the planner chose not to use
>> JIT when it thought there were fewer rows involved.  Did you check
>> with EXPLAIN that these cut-down cases still used JIT?

> I tore these boxes down, so can't check immediately, but I think
> I remember that you're right - single-row queries didn't use JIT.

FWIW, I went to the trouble of installing Ubuntu Focal on my
raspberry pi to see if I could duplicate this, and I couldn't.
However, what you get from a fresh install now is

$ dpkg -l | grep libllvm                  =

ii  libllvm10:arm64                1:10.0.0-4ubuntu1                     a=
rm64        Modular compiler and toolchain technologies, runtime library

not 9.0.1.  I also found that Fedora 31/aarch64 is still downloadable, and
that does contain LLVM 9 ... and I could not reproduce it there either.

So I've run out of things to try.  It still seems like a bug in a specific
point release of LLVM is a possible explanation, especially given that
Debian went so far as to replace that release in an LTS distro.  (The
gcc-related packages are all exactly the same versions as you show.)
I'd believe that data corruption could be a contributing factor too,
except that you were able to read all the rows without JIT.

			regards, tom lane