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Re: Failback with log shipping

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: Failback with log shipping
Date: 2010-05-29 03:11:59
Message-ID: AANLkTik8CRC3Z1WVW2kMyQVbLzDkpQCYpZenY541anr-@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, May 28, 2010 at 7:58 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> At PGCon, several people asked me about restarting an old master as a
> standby after failover has happened. And it wasn't the first time people ask
> me about it, even before 9.0. We have no mention of that in the docs, which
> is a pretty serious oversight. What can we say about it?
>
> I believe the current official policy is that you have to take a new base
> backup and restore from that. Rsync can be used to speed that up.
>
> However, someone once asked me for a comment on a script he wrote to do that
> in a smarter way. I forget who and when and how exactly it worked, but it
> seems possible to do safely.
>
> First of all, you have to shut down the master cleanly for this to work,
> otherwise there can be changes in the old master that never made it to the
> standby.
>
> Assuming controlled shutdown and that the standby received all WAL from the
> old master before it was promoted, I think you can simply create a
> recovery.conf in the old master's data directory to turn it into a standby
> server, and restart. Am I missing something?

Failover always increments the timeline ID of the old standby (i.e.,
new master).
Can that procedure work around the gap of the timeline ID between servers?

Regards,

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

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