Re: backup manifests

On 3/27/20 6:07 PM, Andres Freund wrote:
> Hi,
>
> On 2020-03-27 16:57:46 -0400, Stephen Frost wrote:
>> I really don't know what to say to this. WAL is absolutely critical to
>> a backup being valid. pgBackRest doesn't have a way to *just* validate
>> a backup today, unfortunately, but we're planning to support it in the
>> future and we will absolutely include in that validation checking all of
>> the WAL that's part of the backup.
>
> Could you please address the fact that just about everybody uses base
> backups + later WAL to have a short data loss window? Integrating the
> WAL files necessary to make the base backup consistent doesn't achieve
> much if we can't verify the WAL files afterwards. And fairly obviously
> pg_basebackup can't do much about WAL created after its invocation.
>
> Given that we need something separate to address that "verification
> hole", I don't see why it's useful to have a special case solution (or
> rather multiple ones, for stream and fetch) inside pg_basebackup.

There's a pretty big difference between not being able to play forward
to the end of WAL and not being able to get the backup to restore to
consistency at all.

The WAL that is generated during during the backup has special
importance. Without it you have no backup at all. It's the difference
between *some* data loss and *total* data loss.

Regards,
--
-David
david(at)pgmasters(dot)net