Re: Checksum errors in pg_stat_database

On 12/12/22 5:09 AM, Michael Paquier wrote:
> On Sun, Dec 11, 2022 at 08:48:15PM -0500, Tom Lane wrote:
>> I think a stats table indexed solely by relfilenode wouldn't be a great
>> idea, because you'd lose all the stats about a table as soon as you
>> do vacuum full/cluster/rewriting-alter-table/etc.  Can we create two
>> index structures over the same stats table entries, so you can look
>> up by either relfilenode or OID?  I'm not quite sure how to manage
>> rewrites, where you transiently have two relfilenodes for "the
>> same" table ... maybe we could allow multiple pointers to the same
>> stats entry??
> 
> FWIW, I am not sure that I would care much if we were to dropped the
> stats associated to a relfilenode on a rewrite.  In terms of checksum
> failures, tuples are deformed so if there is one checksum failure a
> rewrite would just not happen.  The potential complexity is not really
> appealing compared to the implementation simplicity and its gains, and
> rewrites are lock-heavy so I'd like to think that people avoid them
> (cough)..

Agree that this is less "problematic" for the checksum use case.
On the other hand, losing IO stats (as the ones we could add later on, suggested by Andres up-thread) looks more of a concern to me.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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