From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Stabilizing the test_decoding checks, take N
Date: Sun, 17 Apr 2022 12:01:53 -0400
Message-ID: <2132311.1650211313@sss.pgh.pa.us> (raw)
In-Reply-To: <20220417143236.lp3hksv2h2z7qn6p@alap3.anarazel.de>
References: <1958043.1650129119@sss.pgh.pa.us>
<20220417143104.eftldj7d73rqtqoc@alap3.anarazel.de>
<20220417143236.lp3hksv2h2z7qn6p@alap3.anarazel.de>
Andres Freund <andres@anarazel.de> writes:
>> On 2022-04-16 13:11:59 -0400, Tom Lane wrote:
>>> We've seen this sort of problem before [2], and attempted to fix it [3]
>>> by making these tests ignore empty transactions. But of course
>>> auto-analyze's transaction wasn't empty, so that didn't help.
>> I don't quite understand this bit - the logic test_decoding uses to
>> decide if a transaction is "empty" is just whether a tuple was
>> output. And there shouldn't be any as part of auto-analyze, because we
>> don't decode catalog changes. I suspect there's something broken in the
>> streaming logic (potentially just in test_decoding) around
>> skip_empty_xacts.
Hmm, I'll defer to somebody who knows that code better about whether
there's an actual bug. However ...
>>> I think the most expedient way to prevent this type of failure is to run
>>> the test_decoding tests with autovacuum_naptime cranked up so far as to
>>> make it a non-issue, like maybe a day.
>> I'm a bit worried about this approach - we've IIRC had past bugs that
>> came only to light because of autovacuum starting. I wonder if we rather
>> should do the opposite and reduce naptime so it'll be seen on fast
>> machines, rather than very slow ones.
It seems likely to me that trying to make a test like this one blind to
autovacuum/autoanalyze activity will make it less useful, not more so.
Why is such blindness desirable?
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, andres@anarazel.de, amit.kapila16@gmail.com, tomas.vondra@enterprisedb.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Stabilizing the test_decoding checks, take N
In-Reply-To: <2132311.1650211313@sss.pgh.pa.us>
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