Re: [HACKERS] make async slave to wait for lsn to be replayed

On Tue, Apr 7, 2020 at 12:58 AM Kartyshov Ivan
<i(dot)kartyshov(at)postgrespro(dot)ru> wrote:
> On 2020-04-04 03:14, Alexander Korotkov wrote:
> > I think that now we would be fine with single LSN and single TIMEOUT.
> > In future we may add multiple LSNs/TIMEOUTs or/and support for
> > expressions as LSNs/TIMEOUTs if we figure out it's necessary.
> >
> > I also think it's good to couple waiting for lsn with beginning of
> > transaction is good idea. Separate WAIT FOR LSN statement called in
> > the middle of transaction looks problematic for me. Imagine we have RR
> > isolation and already acquired the snapshot. Then out snapshot can
> > block applying wal records, which we are waiting for. That would be
> > implicit deadlock. It would be nice to evade such deadlocks by
> > design.
> Ok, here is a new version of patch with single LSN and TIMEOUT.

I think this quite small feature, which already received quite amount
of review. The last version is very pinched. But I think it would be
good to commit some very basic version, which is at least some
progress in the area and could be extended in future. I'm going to
pass trough the code tomorrow and commit this unless I found major
issues or somebody objects.

------
Alexander Korotkov

Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company