I'll be doing a upgrade of a large MySQL 5.0 database to Percona 5.1 and I'm attempting to keep the actual downtime as short as possible during the upgrade, so the regular mysqldump + mysql import procedure doesn't work as well for me as the downtime would be several hours.
Currently I'm running a Master->Slave replication setup (2 servers; 1 master - 1 slave), but the new servers will be master-master-slave (3 servers; 2 masters - 1 slave) managed by MMM.
One approach I'm considering is setting up the new servers to replicate from the old database like this (o-prefix = old server, n-prefix = new server):
oM1 -> oS1
oM1 -> nM1 -> nM2 -> nS1
At the time I'm doing the swap I can then stop the slave on nM1 and shut down oM1 and oS1.
My problem is how do I reliably promote the master-slave setup to master-master so that nM1 changes master to nM2?