>> How can this happen? I always thought, that, when in backup mode,
>> nothing is able to change the database - so the database files shouldn't
>> change. Can autovaccumdb cause the changes?
>>
>
> pg_start_backup() doesn't tell the database to stop writing changes to disk;
> it essentially just says "perform a checkpoint", which means all changes as of
> that instant are written to the base data files. That ensures that you start
> your base backup in a consistent state. When you recover it, replaying the WAL
> files will fix any weirdness in your base backup, and you'll get a working
> database, current up to the last WAL file you recovered.
>
>
I think, I will install a newer version of tar on my cluster. It seems,
that redhat shipped a really old version (1.15.1) with RHEL5. In version
1.16, the return code was changed when an read problem occurs - so I can
differ between an read error and an fatal error.
Thx for your fast help =)