Re: Resetting spilled txn statistics in pg_stat_replication

On Mon, 29 Jun 2020 at 20:37, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Jun 29, 2020 at 10:26 AM Masahiko Sawada
> <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> >
> > On Fri, 26 Jun 2020 at 17:53, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Fri, Jun 26, 2020 at 11:31 AM Masahiko Sawada
> > > <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> > > >
> > > > On Thu, 25 Jun 2020 at 19:35, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > > >
> > > > >
> > > > > Today, I thought about it again, and if we consider the point that
> > > > > logical_decoding_work_mem value doesn’t change much then having the
> > > > > stats at slot-level would also allow computing
> > > > > logical_decoding_work_mem based on stats. Do you think it is a
> > > > > reasonable assumption that users won't change
> > > > > logical_decoding_work_mem for different processes (WALSender, etc.)?
> > > >
> > > > FWIW, if we use logical_decoding_work_mem as a threshold of starting
> > > > of sending changes to a subscriber, I think there might be use cases
> > > > where the user wants to set different logical_decoding_work_mem values
> > > > to different wal senders. For example, setting a lower value to
> > > > minimize the latency of synchronous logical replication to a near-site
> > > > whereas setting a large value to minimize the amount of data sent to a
> > > > far site.
> > > >
> > >
> > > How does setting a large value can minimize the amount of data sent?
> > > One possibility is if there are a lot of transaction aborts and
> > > transactions are not large enough that they cross
> > > logical_decoding_work_mem threshold but such cases shouldn't be many.
> >
> > Yeah, this is what I meant.
> >
> > I agree that it would not be a common case that the user sets
> > different values for different processes. Based on that assumption, I
> > also think having the stats at slot-level is a good idea.
> >
>
> Okay.
>
> > But I might
> > want to have the reset function.
> >
>
> I don't mind but lets fist see how the patch for the basic feature
> looks and what is required to implement it? Are you interested in
> writing the patch for this work?

Yes, I'll write the draft patch.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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