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Re: Incrementally Updated Backups and restartpoints

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Incrementally Updated Backups and restartpoints
Date: 2010-01-13 11:57:37
Message-ID: 3f0b79eb1001130357n6abc8466q6556daf2ab3c3fe2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-docspgsql-hackers
On Wed, Jan 13, 2010 at 8:36 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)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 processing logs shipped from the primary, we will be able to reload that data and restart the standby's recovery process from the last restart point. We no longer need to keep WAL files from before the restart point. If we need to recover, it will be faster to recover from the incrementally updated backup 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,

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

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