Github user tillrohrmann commented on the pull request:
https://github.com/apache/flink/pull/917#issuecomment-123737269
* I chose to call the method `decorateMessage` because it not necessarily
only attaches leader session IDs. In the future we might use this method for
something other than just wrapping the messages in a `LeaderSessionMessage`.
Moreover, calling it `attachSession` would contradict the idea of transparency
here. But we can change it as long as we don't have to do any other decorations.
* The trait `RequiresLeaderSessionID` is only a marker trait which does not
contain any code. Thus, it is effectively equivalent to a Java interface and
in fact Java classes can implement it. The only reason I chose a trait instead
of an interface is that all messages which are sent by the actors are
implemented as Scala classes. I can change it to be an interface, however I
don't think that it cements the language blend.
* I agree that it's not necessary to use mixins here. The reason to
implement the logging and leader session message decoration as a mixin was just
the beauty of the implementation. But I forgot about the clumsy names in the
log output. I will include the mixins in the class `FlinkActor`.
* It is true that the leader session ID can change in the case of HA with
ZooKeeper. However, the ZooKeeper HA is not part of this PR.
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