Re: relfilenode statistics

Hi,

On Thu, Jun 06, 2024 at 08:38:06PM -0700, Andres Freund wrote:
> Hi,
>
> On 2024-06-03 11:11:46 +0000, Bertrand Drouvot wrote:
> > The main argument is that we currently don’t have writes counters for relations.
> > The reason is that we don’t have the relation OID when writing buffers out.
> > Tracking writes per relfilenode would allow us to track/consolidate writes per
> > relation (example in the v1 patch and in the message up-thread).
> >
> > I think that adding instrumentation in this area (writes counters) could be
> > beneficial (like it is for the ones we currently have for reads).
> >
> > Second argument is that this is also beneficial for the "Split index and
> > table statistics into different types of stats" thread (mentioned in the previous
> > message). It would allow us to avoid additional branches in some situations (like
> > the one mentioned by Andres in the link I provided up-thread).
>
> I think there's another *very* significant benefit:
>
> Right now physical replication doesn't populate statistics fields like
> n_dead_tup, which can be a huge issue after failovers, because there's little
> information about what autovacuum needs to do.
>
> Auto-analyze *partially* can fix it at times, if it's lucky enough to see
> enough dead tuples - but that's not a given and even if it works, is often
> wildly inaccurate.
>
>
> Once we put things like n_dead_tup into per-relfilenode stats,

Hm - I had in mind to populate relfilenode stats only with stats that are
somehow related to I/O activities. Which ones do you have in mind to put in
relfilenode stats?

Regards,

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