Message-ID: <47402FE2.5000707@bluegap.ch>
Date: Sun, 18 Nov 2007 13:28:18 +0100
From: Markus Schiltknecht <markus@bluegap.ch>
User-Agent: Mozilla-Thunderbird 2.0.0.6 (X11/20071008)
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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: <200711161541.lAGFf0e29718@momjian.us>
In-Reply-To: <200711161541.lAGFf0e29718@momjian.us>
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Hello Bruce,

Bruce Momjian wrote:
> Uh, I think of PgCluster as multi-master, but in a way it is a hybrid
> because there is a central server that gets all the queries.

Yes, PgCluster as well as Sequoia use statement based replication. 
Sequoia is also clearly a middleware (no changes to Postgres needed).

Both suffer from the limitations you describe in "statement based 
replication middleware". AFAICT Sequoia does quite well in circumventing 
those. (Heck, it even tries to masquerade differences between database 
systems, so you can keep a Postgres database in sync with a MySQL one.)

Depending on the RAIDb level you are using, Sequoia can be considered 
multi-master (RAIDb-1) or single-master (RAIDb-0). Also note that 
sequoia can run multiple controllers, thus it does not rely on one 
central server.

So, at least Sequoia is clearly a hybrid, in between your definitions of 
"statement based replication middleware" and "synchronous multi-master 
replication". Depending on how "middleware" you consider PgCluster, it's 
also a hybrid. Certainly it does statement based replication.

Regards

Markus