Re: Master Master Replication Upgrade from 5.0 to 5.5

[Rick James]

Plan A: Dump the data from 5.0 and load it onto 5.5.
Plan B: Upgrade in place 5.0->5.1, the again for 5.1->5.5.

I hope one master is receiving all writes, and the other is just a hot backup.

Assuming your two machines are on the Left and the Right, serving as Live and Backup, respectively, to start with:
0. Live(50) <-> Backup(50) -- Current config
1. Live(50) --> Backup(50) -- Turn off one replication because replication from newer version to older is not guaranteed to work.
2. Live(50) --> Backup(55) -- upgrade non-Live machine
3. Backup(50) --- Live(55) -- Switch roles; that is, writes are now sent to righthand machine. Also replication is turned off.
4. Backup(55) --- Live(55) -- upgrade non-Live machine
5. Backup(55) <-> Live(55) -- re-establish bi-directional replication
6. Live(55) <-> Backup(55) -- optionally fail back so that the lefthand machine is the live master

At all times (I think), the binlogs need to be written. But you do need to be careful to pick the right binlogs during the CHANGE MASTERs in step 5.

If you also had Slaves hanging off each Master, and you could spare some machines, then I would do this: ('w' represents the one writable master)

w50 <-> 50
w50 <-> 50 --> 55(to-be-master)
w50 <-> 50 --> 55 -> 55(to-be-other-master)
w50 <-> 50 --> 55 -> 55 Hang new 55 slaves off both 55 machines and re-point all read traffic to the 55 slaves. (Pause here to QA.)
50 <-> 50 --> 55 --> 55 stop writes and wait for replication to propagate
50 <-> 50 --> w55 --> 55 re-point write traffic to the 55 master
xx --- xx --- w55 --> 55 Toss old machines
xx --- xx --- w55 <-> 55 Establish bi-directional replication between new masters.