On Mon, May 23, 2022 at 10:03 AM Kyotaro Horiguchi
<horikyota.ntt@gmail.com> wrote:
>
> At Sat, 21 May 2022 15:35:58 +0530, Amit Kapila <amit.kapila16@gmail.com> wrote in
> > I think if we don't have any better ideas then we should go with
> > either this or one of the other proposals in this thread. The other
> > idea that occurred to me is whether we can somehow update the snapshot
> > we have serialized on disk about this information. On each
> > running_xact record when we serialize the snapshot, we also try to
> > purge the committed xacts (via SnapBuildPurgeCommittedTxn). So, during
> > that we can check if there are committed xacts to be purged and if we
> > have previously serialized the snapshot for the prior running xact
> > record, if so, we can update it with the list of xacts that have
> > catalog changes. If this is feasible then I think we need to somehow
> > remember the point where we last serialized the snapshot (maybe by
> > using builder->last_serialized_snapshot). Even, if this is feasible we
> > may not be able to do this in back-branches because of the disk-format
> > change required for this.
> >
> > Thoughts?
>
> I didn't look it closer, but it seems to work. I'm not sure how much
> spurious invalidations at replication start impacts on performance,
> but it is promising if the impact is significant.
>
It seems Sawada-San's patch is doing at each commit not at the start
of replication and I think that is required because we need this each
time for replication restart. So, I feel this will be an ongoing
overhead for spurious cases with the current approach.
> That being said I'm
> a bit negative for doing that in post-beta1 stage.
>
Fair point. We can use the do it early in PG-16 if the approach is
feasible, and backpatch something on lines of what Sawada-San or you
proposed.
--
With Regards,
Amit Kapila.