“Since version 5, MySQL comes with built-in support for
master-master replication, solving the problem that can happen with
self-generated keys. In former MySQL versions, the problem with
master-master replication was that conflicts arose immediately if
node A and node B both inserted an auto-incrementing key on the
same table. The advantages of master-master replication over the
traditional master-slave replication are that you don’t have to
modify your applications to make write accesses only to the master,
and that it is easier to provide high-availability because if the
master fails, you still have the other master…”
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HowtoForge:
MySQL Master Master Replication(Oct 10, 2006)