- client API - must I relink my clients
- datafile - must I dump and reload my database
- replication - can I replicate from a version N master to version N+X slave
- SQL - do statements that work in version N work in version N+X
MySQL states this about replication compatability. I don't have much faith in the support for rolling upgrades after reading this. They should assert there is no problem when replicating to a slave that is one version greater than the master. Are there tests for replication compatability?
As a general rule, you should set up replication only between masters and slaves running the same major versions (5.1, 5.0 or 4.1) of MySQL. If you must execute replication between different major versions, ensure that your client is at a version equal to or higher than that of the master.MySQL docs are clear that datafile compatability is probably not supported on upgrade. I don't mind using dump and restore as that is a one time cost and it is one less thing to worry about.
MySQL recommends that you dump and reload your tables from any previous version to upgrade to 5.1.