Hi, On Wed, Jan 15, 2025 at 06:27:22PM +0900, Michael Paquier wrote: > On Wed, Jan 15, 2025 at 08:30:20AM +0000, Bertrand Drouvot wrote: > > On Wed, Jan 15, 2025 at 11:03:54AM +0300, Nazir Bilal Yavuz wrote: > >> With this commit it may not be possible to count IOs in the critical > >> sections. I think the problem happens only if the local > >> PgStat_BackendPending entry is being created for the first time for > >> this backend in the critical section. > > > > Yeah, I encountered the exact same thing and mentioned it in [1] (see R1.). > > > > In [1] I did propose to use a new PendingBackendWalStats variable to > > "bypass" the > > pgstat_prep_backend_pending() usage. > > > > Michael mentioned in [2] that is not really consistent with the rest (what I > > agree with) and that "we should rethink a bit the way pending entries are > > retrieved". I did not think about it yet but that might be the way to > > go, thoughts? > > > > [1]: > > https://www.postgresql.org/message-id/Z3zqc4o09dM/Ezyz%40ip-10-97-1-34.eu-west-3.compute.internal > > [2]: https://www.postgresql.org/message-id/Z4dRlNuhSQ3hPPv2%40paquier.xyz > > My problem is that this is not only related to backend stats, but to > all variable-numbered stats kinds that require this behavior.
Yeah, agree that it's better to have a "generic" solution. > A generic solution to the problem would be to allow > pgStatPendingContext to have MemoryContextAllowInCriticalSection() set > temporarily for the allocation of the pending data. > Perhaps not for all stats kinds, just for these where we're OK with > the potential memory footprint so we could have a flag in > PgStat_KindInfo. Giving to all stats kinds the responsibility to > allocate a pending entry beforehand outside a critical section is > another option, but that means going through different tweaks for all > stats kinds that require them. > > Andres, do you have any thoughts about that? Not sure what would be > your view on this matter. MemoryContextAllowInCriticalSection() for > stats kinds that allow the case would be OK for me I guess, Same here, that looks ok to me too. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
