Re: Lost replication slots after pg_upgrade.

On Tue, Feb 08, 2022 at 08:32:22AM +0000, Victor Sudakov wrote:
> Julien Rouhaud wrote:
> > 
> > > pg_basebackup takes time for large databases (> 5TB). I feel rsync should
> > > be faster.
> > 
> > Not necessarily.  pg_basebackup will do simple sequential read of all the data,
> > which is probably the fastest thing to do.  rsync will do some extra processing
> > that isn't required in that scenario, so it's likely to be slower (although
> > probably only marginally slower).
> 
> I think Nikhil was going to invoke the rsync black magic as described
> in https://www.postgresql.org/docs/current/pgupgrade.html, not for
> copying the entire PGDATA from the master to standbys. While the rsync
> magic should be hundreds of times faster because only modified files
> will be copied and the majority of files will be just hardlinked, I've
> never felt I have enough skill and luck to undertake this method.

Ah, if that's the case I don't think there's any doubt to have for rsync being
faster.  And this method works just fine if you take care of what you're doing.