Re: Replication slot stats misgivings

On Fri, Apr 16, 2021 at 3:16 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Apr 12, 2021 at 2:57 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > On Sat, Mar 20, 2021 at 9:26 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Sat, Mar 20, 2021 at 12:22 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > >
> > > > And then more generally about the feature:
> > > > - If a slot was used to stream out a large amount of changes (say an
> > > > initial data load), but then replication is interrupted before the
> > > > transaction is committed/aborted, stream_bytes will not reflect the
> > > > many gigabytes of data we may have sent.
> > > >
> > >
> > > We can probably update the stats each time we spilled or streamed the
> > > transaction data but it was not clear at that stage whether or how
> > > much it will be useful.
> > >
> >
> > I felt we can update the replication slot statistics data each time we
> > spill/stream the transaction data instead of accumulating the
> > statistics and updating at the end. I have tried this in the attached
> > patch and the statistics data were getting updated.
> > Thoughts?
> >
>
> Did you check if we can update the stats when we release the slot as
> discussed above? I am not sure if it is easy to do at the time of slot
> release because this information might not be accessible there and in
> some cases, we might have already released the decoding
> context/reorderbuffer where this information is stored. It might be
> okay to update this when we stream or spill but let's see if we can do
> it easily at the time of slot release.
>

I'm not sure if we will be able to update stats from here, as we will
not have access to decoding context/reorderbuffer at this place, and
also like you pointed out I noticed that the decoding context gets
released earlier itself.

Regards,
Vignesh