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Re: Clean shutdown and warm standby

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Clean shutdown and warm standby
Date: 2009-04-27 11:28:12
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers

On Fri, Apr 24, 2009 at 3:20 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> It's not safe to write WAL after the checkpoint, as RequestXLogSwitch()
> does. After restart, the system will start inserting WAL from the checkpoint
> redo point, which is just before the XLOG_SWITCH record, and will overwrite
> it.

Since, in this case, the WAL file including XLOG_SWITCH exists
in archive, I don't think that it's unsafe, i.e. XLOG_SWITCH would
be treated as the last applied record and not be overwritten. WAL
records would start to be inserted from the subsequent file (with
new timeline).

This is useful for warm-standby, but I'm afraid that this may delay
Shared Disk Failover which doesn't need to wait until all the WAL
files are archived at shutdown. Is there any solution to this problem?


Fujii Masao
NTT Open Source Software Center

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