Message-ID: <49EDAB5B.5040400@enterprisedb.com>
Date: Tue, 21 Apr 2009 14:17:47 +0300
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Organization: EnterpriseDB
User-Agent: Mozilla-Thunderbird 2.0.0.19 (X11/20090103)
MIME-Version: 1.0
To: Simon Riggs <simon@2ndQuadrant.com>
CC: Fujii Masao <masao.fujii@gmail.com>,
	Guillaume Smet <guillaume.smet@gmail.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter_e@gmx.net>,
	Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: New trigger option of pg_standby
References: <3f0b79eb0903242329j12865d55s348f5c873a956e71@mail.gmail.com>	
	<1d4e0c10904071456m735e3f67q123b87243d2f6f2a@mail.gmail.com>	
	<3f0b79eb0904071817u5c32254ei61f7e68e54669d9e@mail.gmail.com>	
	<49DDEE72.6030803@enterprisedb.com>	
	<3f0b79eb0904092047w355e0b3ar527a9285b161ef91@mail.gmail.com>	
	<1239381103.16396.30.camel@ebony.2ndQuadrant>	
	<3f0b79eb0904122252t1f4c5860v919d199f399ccf72@mail.gmail.com>	
	<3f0b79eb0904132241p18084914g792cb8e5ab3eebb3@mail.gmail.com>	
	<3f0b79eb0904150101pb1c59a3ubb422867e8e6a944@mail.gmail.com>	
	<49EC3B01.6050509@enterprisedb.com>	
	<3f0b79eb0904200354u41b54017u16dc73d021c03cdb@mail.gmail.com>	
	<49EC8B06.3020204@enterprisedb.com>
	<1240311836.23905.206.camel@ebony.fara.com>
In-Reply-To: <1240311836.23905.206.camel@ebony.fara.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

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