public static String md5PrefixedKey(long key) {
    String stringKey = Long.toString(key);
    String md5hash = MD5Hash.getMD5AsHex(Bytes.toBytes(stringKey));

    // flip the key to randomize
    return md5hash + "-" + stringKey;
  }
Converts the given key to string, and prefixes it with the MD5 hash of the index's string
representation.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/LoadTestKVGenerator.java