1. 散列，建表时分表，然后写入时使用散列函数，将行健打散分布，这样做只是为了写操作多的优化，对于读来说，可能是灾难（全表扫描）
2. salting，使用随机值做前缀，解决散列全表扫描的问题

public static HConnection getConnection(final Configuration conf)
  throws IOException {
    HConnectionKey connectionKey = new HConnectionKey(conf);
    synchronized (CONNECTION_INSTANCES) {
      HConnectionImplementation connection = CONNECTION_INSTANCES.get(connectionKey);
      if (connection == null) {
        connection = (HConnectionImplementation)createConnection(conf, true);
        CONNECTION_INSTANCES.put(connectionKey, connection);
      } else if (connection.isClosed()) {
        HConnectionManager.deleteConnection(connectionKey, true);
        connection = (HConnectionImplementation)createConnection(conf, true);
        CONNECTION_INSTANCES.put(connectionKey, connection);
      }
      connection.incCount();
      return connection;
    }
  }