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Date: Mon, 20 Nov 2006 16:35:25 +0100
From: Markus Schiltknecht <markus@bluegap.ch>
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To: Bruce Momjian <bruce@momjian.us>
CC: Josh Berkus <josh@agliodbs.com>, pgsql-docs@postgresql.org,
	Jim Nasby <decibel@decibel.org>, Jeff Frost <jeff@frostconsultingllc.com>,
	Chris Browne <cbbrowne@acm.org>
Subject: Re: [HACKERS] Replication documentation addition
References: <200611201507.kAKF7AT21962@momjian.us>
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Good morning Bruce,

Bruce Momjian wrote:
>> Oops, I see Markus Schiltknech likes the term "statement-based
>> replication" better too.  Certainly master-slave communication using
>> "statement-based replication" has the same drawbacks as the broadcast
>> method, but I wanted to highlight that the broadcast was happening
>> outside the server.  Do we need a master/slave "statement-based
>> replication" item and a middleware broadcast item?

Ah, I see you had a much narrower definition of statement-based 
replication in mind. As I've pointed out, there are different 
implementations of 'statement-based replication'. I don't know about 
sequoia, but Postgres-R fails back to statement based replication in 
certain situations. Thus having an external 'program intercept every SQL 
query' is absolutely no necessity of this algorithm, it can very well be 
done inside the db backend, where you can better catch non-deterministic 
functions... but again, that's an implementation detail.

So, do you want to describe pgpool here or do you want to give a more 
general description?

>  <varlistentry>
>   <term>Statement-Based Replication</term>
>   <listitem>
> 
>    <para>
>     In statement-based replication, a program intercepts every SQL
>     query and sends it to all servers.  Each server operates
>     independently.  Read-only queries can be sent to a single server
>     because there is no need for all servers to process it.
>    </para>

If you want to go for the general description, I think the 'each server 
operates independently' is somewhere between confusing and false. And 
again, the last sentence applies to all multi-master replication solutions.

Regards

Markus