@Evolving
public interface WriterCommitMessage
extends java.io.Serializable
DataWriter.commit() and will be sent back to the driver side
as the input parameter of BatchWrite.commit(WriterCommitMessage[]) or
StreamingWrite.commit(long, WriterCommitMessage[]).
This is an empty interface, data sources should define their own message class and use it when generating messages at executor side and handling the messages at driver side.