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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Fujii Masao <masao.fujii@gmail.com>
Cc: Guillaume Smet <guillaume.smet@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Peter Eisentraut <peter_e@gmx.net>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: New trigger option of pg_standby
Date: Tue, 21 Apr 2009 14:17:47 +0300
Message-ID: <49EDAB5B.5040400@enterprisedb.com> (raw)
In-Reply-To: <1240311836.23905.206.camel@ebony.fara.com>
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Simon Riggs wrote:
> On Mon, 2009-04-20 at 17:47 +0300, Heikki Linnakangas wrote:
> 
>> At the end of archive recovery, the server always probes for the 
>> timeline by requesting history files until it fails to find one. That 
>> probing should remove the trigger file if it hasn't been removed by 
>> then. It's a bit coincidental to rely on that, but at least it's simple. 
>> The assumption we're making is that the server won't exit recovery 
>> before asking restore_command for a file that doesn't exist.
> 
> If you really want to simplify this, then we should have a final_command
> parameter for a command to be executed at the end of recovery. That
> would make the change to pg_standby very simple and allow for a very
> simple final_command also. That would make the logic similar to what we
> do for aggregates: transition function and final function. 
> 
> We could call it restore_cleanup_command or something similar.

Hmm, that might indeed be a cleaner interface. However, that throws the 
idea of backpatching out of the window, and will make it impossible to 
run a PG 8.4 pg_standby against a PG 8.3 server. Do we want to add the 
new parameter for 8.4 anyway?

> I suspect this option will make you consider Fujii-san's patch in a
> better light. :-)

No, removing trigger file as soon as a non-existant file is requested 
still seems simpler than deleting it whenever a timeline history file is 
requested.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com



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