Re: Safe switchover

Hi Stephen,

> On 13. Jul, 2020, at 18:00, Stephen Frost <sfrost@snowman.net> wrote:
>
> A pgbackrest delta restore will scan the entire data directory and
> verify every file matches the last backup, or it'll replace the file
> with what was in the backup that's being used.  If there's an error
> during any of that, the restore will fail.

ok, I didn't know that. Thanks very much. I'll look into it.

> That re-validation of the entire data directory is a pretty huge
> difference compared to how pg_rewind works.

I agree.

> Ah, yes, if you rebuild the replica from a backup (or from the primary),
> then sure, that's pretty similar to the pgbackrest delta restore, except
> that when using delta restore we're only rewriting files that have a
> different SHA checksum after being scanned, and we're pulling from the
> backup repo anything that's needed and not putting load on the primary.

so, from what I understand, pgbackrest bottom line merely reduces copy overhead in such a particular case. *Kind of*
likeshutdown primary, rsync, and then startup. 

> There's been a few discussions on -hackers about this, that'd probably
> be the place to discuss it further..

I'm not hacker, I'm just a DBA. :-)

Cheers,
Paul