From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com> |
Cc: | "Yu Shi (Fujitsu)" <shiy(dot)fnst(at)fujitsu(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, tomas(dot)vondra(at)enterprisedb(dot)com, Andres Freund <andres(at)anarazel(dot)de> |
Subject: | Re: BF animal dikkop reported a failure in 035_standby_logical_decoding |
Date: | 2023-05-29 11:03:05 |
Message-ID: | 95382.1685358185@sss.pgh.pa.us |
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"Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com> writes:
> On 5/26/23 9:27 AM, Yu Shi (Fujitsu) wrote:
>> Is it possible that the vacuum command didn't remove tuples and then the
>> conflict was not triggered?
> The flush_wal table added by Andres should guarantee that the WAL is flushed, so
> the only reason I can think about is indeed that the vacuum did not remove tuples (
> but I don't get why/how that could be the case).
This test is broken on its face:
CREATE TABLE conflict_test(x integer, y text);
DROP TABLE conflict_test;
VACUUM full pg_class;
There will be something VACUUM can remove only if there were no other
transactions holding back global xmin --- and there's not even a delay
here to give any such transaction a chance to finish.
Background autovacuum is the most likely suspect for breaking that,
but I wouldn't be surprised if something in the logical replication
mechanism itself could be running a transaction at the wrong instant.
Some of the other recovery tests set
autovacuum = off
to try to control such problems, but I'm not sure how much of
a solution that really is.
regards, tom lane
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