Re: pg_stat_io for the startup process

At Sun, 21 May 2023 15:14:23 -0700, Andres Freund <andres(at)anarazel(dot)de> wrote in
> Hi,
>
> I don't really feel confident we're going to get the timeout approach solid
> enough for something going into the tree around beta 1.
>
> How about this, imo a lot simpler, approach: We flush stats whenever replaying
> a XLOG_RUNNING_XACTS record. Unless the primary is idle, it will log those at
> a regular interval. If the primary is idle, we don't need to flush stats in
> the startup process, because we'll not have done any io.
>
> We only log XLOG_RUNNING_XACTS when wal_level >= replica, so stats wouldn't
> get regularly flushed if wal_level = minimal - but in that case the stats are
> also not accessible, so that's not a problem.

I concur with the three aspects, interval regularity, reliability and
about the case of the minimal wal_level. While I can't confidently
claim it is the best, its simplicilty gives us a solid reason to
proceed with it. If necessary, we can switch to alternative timing
sources in the future without causing major disruptions for users, I
believe.

> It's not the prettiest solution, but I think the simplicity is worth a lot.
>
> Greetings,

+1.

--
Kyotaro Horiguchi
NTT Open Source Software Center