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Re: Replication for migration

From: Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
To: martins(dot)listz(at)gmail(dot)com
Cc: Kenneth Marshall <ktm(at)rice(dot)edu>, pgsql-admin(at)postgresql(dot)org
Subject: Re: Replication for migration
Date: 2009-05-14 14:39:25
Message-ID: 87vdo392aq.fsf@hi-media-techno.com (view raw or flat)
Thread:
Lists: pgsql-admin
Hi,

Martin Spinassi <martins(dot)listz(at)gmail(dot)com> writes:
> On Thu, 2009-05-14 at 08:59 -0500, Kenneth Marshall wrote:
>> I used Slony replication to upgrade a database from 8.2 -> 8.3 and
>> it worked quite well. You will need an outage to change the master
>> to the 8.3 database and re-point your apps, but if scripted, that
>> is minimal.
>
> I've seen that slony documentation is huge! I'll give it a shot in
> testing environment.

The skytools project's documentation is an easy read ;)
  http://wiki.postgresql.org/wiki/Londiste_Tutorial

Londiste in its current stable version (2.1.9) doesn't support failover,
but as long as you're migrating away from 8.2 I suppose you don't need
to be able to switch back.

The procedure would then be:
 - setup londiste and replicate data
 - enter site maintenance mode (no more writes on the database)
 - wait for the londiste logs to show there's nothing to replicate
   (while waiting, maybe setup the site to point to 8.3)
 - open up the site again, on 8.3
 - shut down the londiste daemons and the 8.2 pg server

The waiting for emptying queues shouldn't be very long, expect 3s to
30s, but be sure to test it before switching for real, of course.

Regards,
-- 
dim

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