@Override public void write(DataOutput out) throws IOException {
    super.write(out);
    out.writeUTF(druidQuery);
    out.writeInt(hosts.length);
    for (String host : hosts) {
      out.writeUTF(host);
    }
  }
Druid split. Its purpose is to trigger query execution in Druid.
druid-handler/src/java/org/apache/hadoop/hive/druid/io/HiveDruidSplit.java