Subject: Re: Infrastructure changes for recovery
From: Simon Riggs <simon@2ndquadrant.com>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
In-Reply-To: <20080807145610.GD4171@alvh.no-ip.org>
References: <1218109459.4549.423.camel@ebony.2ndQuadrant>
	<20080807145610.GD4171@alvh.no-ip.org>
Content-Type: text/plain
Date: Thu, 07 Aug 2008 17:05:14 +0100
Message-Id: <1218125114.4549.562.camel@ebony.2ndQuadrant>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit


On Thu, 2008-08-07 at 10:56 -0400, Alvaro Herrera wrote:
> Simon Riggs wrote:

> > ii) have postmaster allow connections while Redo is taking place, as
> one
> > part of allowing query access to standby database
> 
> is interesting and I'm sure it would be very welcome.  Of course, it
> is first necessary to be able to run transactions in true "read only"
> mode, which perhaps is nowadays not so difficult given the work with
> VXids.

Maybe I am assuming that part is easier than I thought. Florian's
contribution with the VXid work should not be understated.

I was going to spread the setting of the global variable InRedo to all
backends, so they would be able to answer the question IsInRedo().

Anybody attempting to assign a new TransactionId would check this and
then exit with an ERROR. There would also be a check in XLogInsert(), in
case the first case doesn't catch everything or everyone. Transactions
would also run as read-only transactions to keep the front door locked.

Anything else you think needs bolting down?

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support