@Override
  public String toString() {
    return String.format("KafkaCheckpointLogKey[factoryClass: %s, taskName: %s, type: %s]",
        grouperFactoryClassName, taskName, type);
  }
Two {@link KafkaCheckpointLogKey}s are equal iff their grouperFactory class, taskName and type are equal.
samza-kafka/src/main/java/org/apache/samza/checkpoint/kafka/KafkaCheckpointLogKey.java