Re: Show WAL write and fsync stats in pg_stat_io

On Tue, Nov 07, 2023 at 03:30:48PM -0800, Andres Freund wrote:
> I strongly disagree. A significant part of the design of pg_stat_io was to
> make it possible to collect multiple sources of IO in a single view, so that
> sysadmins don't have to look in dozens of places to figure out what is causing
> what kind of IO.

Okay. Point taken.

> We should over time collect all sources of IO in pg_stat_io. For some things
> we might want to also have more detailed information in other views (e.g. it
> doesn't make sense to track FPIs in pg_stat_io, but does make sense in
> pg_stat_wal) - but that should be in addition, not instead of.

Sure. I understand here that you mean the number of FPIs counted when
a record is inserted, different from the path where we decide to write
and/or flush WAL. The proposed patch seems to be a bit inconsistent
regarding wal_sync_time, by the way.

By the way, if the write/sync quantities and times begin to be tracked
by pg_stat_io, I'd see a pretty good argument in removing the
equivalent columns in pg_stat_wal. It looks like this would reduce
the confusion related to the handling of PendingWalStats added in
pgstat_io.c, for one.
--
Michael