This manual is for an old version of Hazelcast Jet, use the latest stable version.

Special care must be taken when serializing Writable items. The hazelcast-jet-hadoop module implements out-of-the-box serialization support for some of the primitive types including the following:

  • BooleanWritable
  • ByteWritable
  • DoubleWritable
  • FloatWritable
  • IntWritable
  • LongWritable
  • Text

Anything outside of these types falls back to a default implementation for all Writable types which writes the full class name and the fields per item. When deserializing, the class name is read first and the deserialized instance is created using the classloader and reflection. The explicitly registered types only write a single integer as a type id and do not use reflection for deserialization.

To explicitly register your own Writable types for fast serialization, you can extend the provided WritableSerializerHook class and register the hook with Hazelcast.