Sorry for just getting a chance to look at this patch now. For https://issues.apache.org/jira/browse/AVRO-261 I noticed that properties are still mutable.
Any chance we could lock that down? Or add the option to lock it down. Eg a lockProps() method which sets a boolean and after being called, calls to setProp would throw an AvroRuntimeException. I could throw together a patch (it would also make the props member variable private) if this seems reasonable. It would be nice to complete this for 1.3, but certainly not a blocker.
