Re: Is Recovery actually paused?

On Tue, Oct 20, 2020 at 3:00 PM Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>
> On Tue, 20 Oct 2020 at 09:50, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> > > > Why would we want this? What problem are you trying to solve?
> > >
> > > The requirement is to know the last replayed WAL on the standby so
> > > unless we can guarantee that the recovery is actually paused we can
> > > never get the safe last_replay_lsn value.
> > >
> > > > If we do care, why not fix pg_is_wal_replay_paused() so it responds as you wish?
> > >
> > > Maybe we can also do that but pg_is_wal_replay_paused is an existing
> > > API and the behavior is to know whether the recovery paused is
> > > requested or not, So I am not sure is it a good idea to change the
> > > behavior of the existing API?
> > >
> >
> > Attached is the POC patch to show what I have in mind.
>
> If you don't like it, I doubt anyone else cares for the exact current
> behavior either. Thanks for pointing those issues out.
>
> It would make sense to alter pg_wal_replay_pause() so that it blocks
> until paused.
>
> I suggest you add the 3-value state as you suggest, but make
> pg_is_wal_replay_paused() respond:
> if paused, true
> if requested, wait until paused, then return true
> else false
>
> That then solves your issues with a smoother interface.
>

Make sense to me, I will change as per the suggestion.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com