Message-ID: <4746D3D2.2080809@bluegap.ch>
Date: Fri, 23 Nov 2007 14:21:22 +0100
From: Markus Schiltknecht <markus@bluegap.ch>
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To: Bruce Momjian <bruce@momjian.us>
CC: PostgreSQL-documentation <pgsql-docs@postgresql.org>
Subject: Re: High Availability, Load Balancing, and Replication Feature Matrix
References: <200711192121.lAJLLAi07431@momjian.us>
In-Reply-To: <200711192121.lAJLLAi07431@momjian.us>
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Hello Bruce,

Bruce Momjian wrote:
> Uh, to me the issue is something like pgpool and Sequoia, where the
> _master_/replication is happening _outside_ the server

Well, you are saying that the controllers are the masters and do 
replication. I can see the reasoning behind it: they are the only nodes 
  which allow write access, seen from the outside.

However, I don't consider these controllers to be masters nor slaves, 
because they don't carry a replica of the data. Instead I'm considering 
the database nodes which are (synchronously or not) processing the 
writing transactions on behalf of the controller to be the masters. They 
do all the work and the locking, and they carry the replicated data.

PgCluster (and therefore Cybercluster, too) seem to follow my 
definition, as they are advertising themselves as multi-master 
replication solutions (even though they only support one single 
controller, AFAICT).

I didn't find any self-definition of PgPool's replication feature nor 
Sequoias. However, I'd argue that both are generally considered 
synchronous multi-master replication solutions as well, even if there's 
only one controller.

 > vs something
 > like Oracle RAC where it is happening inside the server.

..or like Postgres-R :-)

Regards

Markus