Re: Do results of pg_start_backup work without WAL segments created during backup?

> On Jul 8, 2019, at 7:10 AM, Thorsten Schöning <tschoening(at)am-soft(dot)de> wrote:
>
> "since the last checkpoint": Missing WAL-segments mean a loss of data
> only. It doesn't mean that formerly "checkpointed" data gets magically
> broken, else crash recovery wouldn't work like described in the docs.

Not true. The database files are probably written to between checkpoints, and certainly during subsequent checkpoints which may occur during the backup.

> I don't see how WAL-archives created between pg_start- and
> pg_stop_backup are any different to later ones.

They are necessary to straighten out changes that were occurring during the backup.

> If I backup some VM using snapshots, I don't
> necessarily care about the changes made within the VM during the
> backup as well.

A snapshot is an entirely different thing, since it's an atomic grab of state at one point, very different than sequentially copying files while they are being modified in a order that is in no way related to the order of copying.