Hi all! Flink 1.4 introduces child-first classloading by default, for the application libraries.
We added that, because it allows applications to use different versions of many libraries, compared to what Flink uses in its core, or compared to what other dependencies (like Hadoop) pull into the class path. For example, applications can use different versions of akka, Avro, Protobuf, etc. Compared to what Flink / Hadoop / etc. uses. Now, while that is nice, child-first classloading runs into trouble when the application jars are not properly built, meaning when the application JAR contains libraries that it should not (because they are already in the classpath / lib folder). For example, when the class path has the Kafka Connector (connector is in the lib directory) and the application jar also contains Kafka, the we get nasty errors due to class duplication and impossible class casts (X cannot be cast to X). What I would like to understand is how this change worked out for the users. Based on that, we can keep this or revert this change in the next release. Please answer to this mail with: a. This was a great change, keep it and polish it. b. This caused in the end more problems than it solved, so please set the default back to "parent-first" in 1.5 and leave "child-first" as an optional flag. Thanks a lot, Stephan
