Thread: Continuous archiving and wal generation

Hello list

I have a question concerning the continuous archiving process. The manual says:

To make use of the backup, you will need to keep around all the WAL segment files generated during and after the file system backup. To aid you in doing this, the pg_stop_backup function creates a backup history file that is immediately stored into the WAL archive area. This file is named after the first WAL segment file that you need to have to make use of the backup. For example, if the starting WAL file is 0000000100001234000055CD the backup history file will be named something like 0000000100001234000055CD.007C9330.backup .

My question is: if I have a large database which takes some time to backup with tar, and during the interval between pg_start_backup() and pg_stop_backup() more than one wal file gets generated, do I have to store in addition to the base backup all wal files generated during the backup interval or just the one specified by the .backup file?

I'm trying to figure out the minimum required to restore from a backup, and my common sense says that I should archive all the wal files produced during the backup since they contain information of the data file changes made during the backup.

Regards

M

>>> On Fri, Oct 19, 2007 at  1:40 AM, in message
<2ca799770710182340y9877687i8e82cd6847f37c5a@mail.gmail.com>, "Mikko Partio"
<mpartio@gmail.com> wrote:
>
> To make use of the backup, you will need to keep around all the WAL segment
> files generated during and after the file system backup. To aid you in doing
> this, the pg_stop_backup function creates a *backup history file* that is
> immediately stored into the WAL archive area. This file is named after the
> first WAL segment file that you need to have to make use of the backup. For
> example, if the starting WAL file is 0000000100001234000055CD the backup
> history file will be named something like
> 0000000100001234000055CD.007C9330.backup.
>
> My question is: if I have a large database which takes some time to backup
> with tar, and during the interval between pg_start_backup() and
> pg_stop_backup() more than one wal file gets generated, do I have to store
> in addition to the base backup all wal files generated during the backup
> interval or just the one specified by the .backup file?
>
> I'm trying to figure out the minimum required to restore from a backup

If you look inside that backup file, you'll see something like this:

START WAL LOCATION: 47/11B7E980 (file 000000010000004700000011)
STOP WAL LOCATION: 47/13006410 (file 000000010000004700000013)
CHECKPOINT LOCATION: 47/11B7E980
START TIME: 2007-10-12 19:00:02 CDT
LABEL: 2007-10-12_190002
STOP TIME: 2007-10-12 20:10:30 CDT

It tells you what files  you need, as a minimum, to restore.

-Kevin