Re: Resetting spilled txn statistics in pg_stat_replication

On Thu, 11 Jun 2020 at 18:11, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Jun 11, 2020 at 1:46 PM Masahiko Sawada
> <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> >
> > On Thu, 11 Jun 2020 at 12:30, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > >
> > > Now, thinking about this again, I am not sure if these stats are
> > > directly related to slots. These are stats for logical decoding which
> > > can be performed either via WALSender or decoding plugin (via APIs).
> > > So, why not have them displayed in a new view like pg_stat_logical (or
> > > pg_stat_logical_decoding/pg_stat_logical_replication)? In future, we
> > > will need to add similar stats for streaming of in-progress
> > > transactions as well (see patch 0007-Track-statistics-for-streaming at
> > > [1]), so having a separate view for these doesn't sound illogical.
> > >
> >
> > I think we need to decide how long we want to remain these statistics
> > values. That is, if we were to have such pg_stat_logical view, these
> > values would remain until logical decoding finished since I think the
> > view would display only running logical decoding. OTOH, if we were to
> > correspond these stats to slots, these values would remain beyond
> > multiple logical decoding SQL API calls.
> >
>
> I thought of having these till the process that performs these
> operations exist. So for WALSender, the stats will be valid till it
> is not restarted due to some reason or when performed via backend, the
> stats will be valid till the corresponding backend exits.
>

The number of rows of that view could be up to (max_backends +
max_wal_senders). Is that right? What if different backends used the
same replication slot one after the other?

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services