rcfile/src/main/java/com/twitter/elephantbird/mapreduce/output/RCFileProtobufOutputFormat.java
public static void setClassConf(Class<? extends Message> protoClass, Configuration conf) {
    Protobufs.setClassConf(conf, RCFileProtobufOutputFormat.class, protoClass);
  }
public static void setClassConf(Class<? extends Message> protoClass, Configuration conf) {
    Protobufs.setClassConf(conf, RCFileProtobufOutputFormat.class, protoClass);
  }
Stores supplied class name in configuration. This configuration is
read on the remote tasks to initialize the output format correctly.