RE: Synchronizing slots from primary to standby

On Thursday, February 15, 2024 5:20 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Thu, Feb 15, 2024 at 9:05 AM Zhijie Hou (Fujitsu) <houzj(dot)fnst(at)fujitsu(dot)com>
> wrote:
> >
> > On Thursday, February 15, 2024 10:49 AM Amit Kapila
> <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Wed, Feb 14, 2024 at 7:26 PM Bertrand Drouvot
> > >
> > > Right, we can do that or probably this test would have made more
> > > sense with a worker patch where we could wait for the slot to be synced.
> > > Anyway, let's try to recreate the slot/subscription idea. BTW, do
> > > you think that adding a LOG when we are not able to sync will help
> > > in debugging such problems? I think eventually we can change it to
> > > DEBUG1 but for now, it can help with stabilizing BF and or some other
> reported issues.
> >
> > Here is the patch that attempts the re-create sub idea.
> >
>
> Pushed this.
>
> >
> I also think that a LOG/DEBUG
> > would be useful for such analysis, so the 0002 is to add such a log.
> >
>
> I feel such a LOG would be useful.
>
> + ereport(LOG,
> + errmsg("waiting for remote slot \"%s\" LSN (%X/%X) and catalog xmin"
> + " (%u) to pass local slot LSN (%X/%X) and catalog xmin (%u)",
>
> I think waiting is a bit misleading here, how about something like:
> "could not sync slot information as remote slot precedes local slot:
> remote slot \"%s\": LSN (%X/%X), catalog xmin (%u) local slot: LSN (%X/%X),
> catalog xmin (%u)"

Changed.

Attach the v2 patch here.

Apart from the new log message. I think we can add one more debug message in
reserve_wal_for_local_slot, this could be useful to analyze the failure. And we
can also enable the DEBUG log in the 040 tap-test, I see we have similar
setting in 010_logical_decoding_timline and logging debug1 message doesn't
increase noticable time on my machine. These are done in 0002.

Best Regards,
Hou zj