Re: Replication slot stats misgivings

On Tue, Apr 27, 2021 at 11:45 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Tue, Apr 27, 2021 at 8:01 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > On Mon, Apr 26, 2021 at 8:42 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Apr 26, 2021 at 8:01 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > > On Fri, Apr 23, 2021 at 6:15 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > > >
> > > > > On Mon, Apr 19, 2021 at 4:28 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > > > > >
> > > > > > I have made the changes to update the replication statistics at
> > > > > > replication slot release. Please find the patch attached for the same.
> > > > > > Thoughts?
> > > > > >
> > > > >
> > > > > Thanks, the changes look mostly good to me. The slot stats need to be
> > > > > initialized in RestoreSlotFromDisk and ReplicationSlotCreate, not in
> > > > > StartupDecodingContext. Apart from that, I have moved the declaration
> > > > > of UpdateDecodingStats from slot.h back to logical.h. I have also
> > > > > added/edited a few comments. Please check and let me know what do you
> > > > > think of the attached?
> > > >
> > > > The patch moves slot stats to the ReplicationSlot data that is on the
> > > > shared memory. If we have a space to store the statistics in the
> > > > shared memory can we simply accumulate the stats there and make them
> > > > persistent without using the stats collector?
> > > >
> > >
> > > But for that, we need to write to file at every commit/abort/prepare
> > > (decode of commit) which I think will incur significant overhead.
> > > Also, we try to write after few commits then there is a danger of
> > > losing them and still there could be a visible overhead for small
> > > transactions.
> > >
> >
> > I preferred not to persist this information to file, let's have stats
> > collector handle the stats persisting.
> >
>
> Sawada-San, I would like to go ahead with your
> "Use-HTAB-for-replication-slot-statistics" unless you think otherwise?

I agree that it's better to use the stats collector. So please go ahead.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/