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Date: Wed, 13 Jan 2010 20:57:37 +0900
Message-ID: <3f0b79eb1001130357n6abc8466q6556daf2ab3c3fe2@mail.gmail.com>
Subject: Re: Incrementally Updated Backups and restartpoints
From: Fujii Masao <masao.fujii@gmail.com>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Wed, Jan 13, 2010 at 8:36 PM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> Our documentation suggests that you can take a base backup of a warm
> standby server while it's running:
>
>> If we take a backup of the standby server's data directory while it is p=
rocessing logs shipped from the primary, we will be able to reload that dat=
a and restart the standby's recovery process from the last restart point. W=
e no longer need to keep WAL files from before the restart point. If we nee=
d to recover, it will be faster to recover from the incrementally updated b=
ackup than from the original base backup.
>
> That doesn't seem safe. If the server makes a new restartpoint while the
> backup is running, and pg_control is backed up after the new
> restartpoint is made, recovery will restart from the new restartpoint.
> That is wrong; recovery needs to restart at the restartpoint that was
> most recent when the backup started. This is basically the same issue we
> have solved in master with the backup_label file.

Right.

> I wonder if it would be enough to document that pg_control must be
> backed up first?

Probably No. The archive recovery from such base backup would always
fail at the end of recovery because there is no backup-end record,
i.e., pg_stop_backup() is not executed in that case.

Regards,

--=20
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center