public void flushBlock(KeyBuffer keyBuffer, ValueBuffer valueBuffer,
        int recordLen, int keyLength,
        @SuppressWarnings("unused") int compressedKeyLen) throws IOException {
      writeKey(keyBuffer, recordLen, keyLength);
      valueBuffer.write(out);
    }
flush a block out without doing anything except compressing the key part.
ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java