From: Rik Wasmus
Date: August 3 2011 10:38am
Subject: Re: does mysql support master to master replication
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Message-Id: <201108031238.51874.rik@grib.nl>
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> Any mysql instance can replicate from any other as long as binary logging
> is enabled on the designated master.
> Two instances can replicate from one another yes, but precautions must be
> taken especially in the case of active-active configuration.

Works perfectly indeed, to name the precautions to take:

1, Set proper server_id's

2. When using auto-incrementing fields, set the auto_increment_offset & 
auto_increment_increment.

3. If you write on 2 servers simultaneously, UNIQUE indexes can break 
replication. If your application requires both enforcing them AND writing to 
both servers, look at clustering instead.
-- 
Rik Wasmus