Horton

Re: BUG #17804: Assertion failed in pg_stat after fetching from pg_stat_database and switching cache->snapshot

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, pgsql-bugs@lists.postgresql.org
Date: 2023-04-27T10:00:00Z
Lists: pgsql-bugs

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Hello,

24.02.2023 19:00, Alexander Lakhin wrote:
> Hello Kyotaro-san,
> 24.02.2023 10:08, Kyotaro Horiguchi wrote:
>> Thanks for the report!  We didn't consider the case that variable is
>> changed in-transaction.
>>
>>
>> What are your thoughts on this?
> What if we implement assign_pgstat_fetch_consistency() and execute
> pgstat_clear_snapshot() in it when the mode switch happens (to avoid
> possible inconsistency between the GUC and the current pgstat state)?

Please look at the attached patch, which implements that idea and also
includes a simple test. The behavior change doesn't affect any of existing
tests and seems natural to me, so I haven't added a note about it in the docs.

Best regards,
Alexander

Commits

  1. Fix assertion failure when updating stats_fetch_consistency in a transaction

  2. Document values of stats_fetch_consistency in postgresql.conf.sample