Re: Checksum errors in pg_stat_database

On 12/12/22 12:40 AM, Michael Paquier wrote:
> On Sun, Dec 11, 2022 at 09:18:42PM +0100, Magnus Hagander wrote:
>> It would be less of a concern yes, but I think it still would be a concern.
>> If you have a large amount of corruption you could quickly get to millions
>> of rows to keep track of which would definitely be a problem in shared
>> memory as well, wouldn't it?
>
> Yes. I have discussed this item with Bertrand off-list and I share
> the same concern. This would lead to an lot of extra workload on a
> large seqscan for a corrupted relation when the stats are written
> (shutdown delay) while bloating shared memory with potentially
> millions of items even if variable lists are handled through a dshash
> and DSM.
>
>> But perhaps we could keep a list of "the last 100 checksum failures" or
>> something like that?
>
> Applying a threshold is one solution. Now, a second thing I have seen
> in the past is that some disk partitions were busted but not others,
> and the current database-level counters are not enough to make a
> difference when it comes to grab patterns in this area. A list of the
> last N failures may be able to show some pattern, but that would be
> like analyzing things with a lot of noise without a clear conclusion.
> Anyway, the workload caused by the threshold number had better be
> measured before being decided (large set of relation files with a full
> range of blocks corrupted, much better if these are in the OS cache
> when scanned), which does not change the need of a benchmark.
>
> What about just adding a counter tracking the number of checksum
> failures for relfilenodes

Agree about your concern for tracking the corruption for every single block.
I like this idea for relfilenodes tracking instead. Indeed it looks like this is enough useful historical information to work with.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com