void writeFileHeader() throws IOException {
      if (useNewMagic) {
        out.writeBoolean(isCompressed());
      } else {
        Text.writeString(out, KeyBuffer.class.getName());
        Text.writeString(out, ValueBuffer.class.getName());
        out.writeBoolean(isCompressed());
        out.writeBoolean(false);
      }

      if (isCompressed()) {
        Text.writeString(out, (codec.getClass()).getName());
      }
      metadata.write(out);
    }
Write and flush the file header.
ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java