Re: per backend I/O statistics

Hi,

On Tue, Sep 03, 2024 at 04:07:58PM +0900, Kyotaro Horiguchi wrote:
> At Tue, 03 Sep 2024 15:37:49 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > When I first looked at this patch, my initial thought was whether we
> > should let these stats stay "fixed." The reason why the current
> > PGSTAT_KIND_IO is fixed is that there is only one global statistics
> > storage for the entire database. If we have stats for a flexible
> > number of backends, it would need to be non-fixed, perhaps with the
> > entry for INVALID_PROC_NUMBER storing the global I/O stats, I
> > suppose. However, one concern with that approach would be the impact
> > on performance due to the frequent creation and deletion of stats
> > entries caused by high turnover of backends.
>
> As an additional benefit of this approach, the client can set a
> connection variable, for example, no_backend_iostats to true, or set
> its inverse variable to false, to restrict memory usage to only the
> required backends.

Thanks for the feedback!

If we were to add an on/off switch button, I think I'd vote for a global one
instead. Indeed, I see this feature more like an "Administrator" one, where
the administrator wants to be able to find out which session is reponsible of
what (from an I/O point of view): like being able to anwser "which session is
generating this massive amount of reads"?

If we allow each session to disable the feature then the administrator
would lost this ability.

Regards,

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