Re: several questions about pg_dumpall, pg_start_backup, pg_basebackup and WAL

Patrick Dung <patrick_dkt@yahoo.com.hk> wrote:
> Albe Laurenz <laurenz.albe@wien.gv.at>
>> Patrick Dung wrote:

>>> It is possible that there is file changes (added or file size
>>> changed) between the pg_start_backup and pg_stop_backup.
>>
>> Yes.
>>
>>> Is the backup consistent?
>>
>> The tar or snapshot itself will not be consistent, it will have
>> to be recovered at least until the end on the online backup.
>
> I should ask: is the backup crash consistent?

PITR restore procedures will use the crash recovery mechanism to
make the database consistent, if that's what you mean.

> Which means it is consistent at the time that the pg_start_backup
> is run.

No.  It will be consistent with the time that pg_stop_backup was
run, or any later point in time that you choose, as long as you
have WAL to that point in time.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company