HBase概念学习（九）HTablePool为何弃用？

原文  http://blog.csdn.net/jiyiqinlovexx/article/details/36526433

主题 HBase

我们先看HConnection的getTable方法描述：

• getTable

  HTableInterface getTable(String tableName)
                           throws IOException

  Retrieve an HTableInterface implementation for access to a table. The returned HTableInterface is not thread safe, a new instance should be created for each using thread. This is a lightweight operation, pooling or caching of the returned HTableInterface is neither required nor desired. Note that the HConnection needs to be unmanaged (created withHConnectionManager.createConnection(Configuration) ).

  Parameters:

  tableName -

  Returns:

  an HTable to use for interactions with this table

  Throws:

  IOException

上面说HTable的的父类HTableInterface是非线程安全的，针对每个线程建议都应该创建一个新的HTableInterface实例，这个创建过程是轻量的，缓存HTableInterface对象既不是必须的也不是推荐的！

然后再联想到只要HTable使用的Configuration是同一个，那么它们一定是共用一个HConnection的，HConnection才是HBase客户端到Hbase集群的真正的连接。

再想想HTablePool的作用，无非就是HTable的连接池，里面维护的HTable应该来说都是使用的同一个HConnecion。

既然HTable的创建是轻量级的，使用同一个Confuguration的HTable都会共用一个HConnection，那么HTablePool就显得那么多余！

所以Hbase抛弃了HTablePool，我们唯一要做的就是保证HConnection实例是唯一的，全局共享的。然后针对HTableInterface对象最好在每次操作HBase表的时候根据HConnection对象来重新创建，使用完成之后及时关闭即可！

通过HConnection的getTable()方法就能够获取到用户操作HBase表的HTableInterface对象了。

下面是一个使用HConnection的getTable()方法获取HTableInterface对象的例子：

public void addUser(User user) throws IOException 
  {
    HTableInterface usersTable = conn.getTable(TABLE_NAME);
    
    Put put = makePut(user);		
    usersTable.put(put);
    
    usersTable.close();
    log.info("Add a User:"+user.name+" successfully");
  }

至于HConnection对象如何创建，HBase推荐使用的方法是：

• createConnection

  public static HConnection createConnection(org.apache.hadoop.conf.Configuration conf)
                                      throws IOException

  Create a new HConnection instance using the passed conf instance.

  Note: This bypasses the usual HConnection life cycle management done bygetConnection(Configuration) . The caller is responsible for callingCloseable.close() on the returned connection instance. This is the recommended way to create HConnections. HConnection connection = HConnectionManager.createConnection(conf); HTableInterface table = connection.getTable("mytable"); table.get(...); ... table.close(); connection.close();

  Parameters:

  conf - configuration

  Returns:

  HConnection object for conf

  Throws:

  ZooKeeperConnectionException

  IOException

下面代码是我按照单例模式维护HConnection对象的例子：

public class HBaseUtils {

  private static final String QUORUM = "192.168.1.100";
  private static final String CLIENTPORT = "2181";
  private static Configuration conf = null;
  private static HConnection conn = null;
  
  /**
   * 获取全局唯一的Configuration实例
   * @return
   */
  public static synchronized Configuration getConfiguration()
  {		
    if(conf == null)
    {
      conf =  HBaseConfiguration.create();
      conf.set("hbase.zookeeper.quorum", QUORUM); 
      conf.set("hbase.zookeeper.property.clientPort", CLIENTPORT);			
    }		
    return conf;				
  }
  
  /**
   * 获取全局唯一的HConnection实例
   * @return
   * @throws ZooKeeperConnectionException
   */
  public static synchronized HConnection getHConnection() throws ZooKeeperConnectionException
  {
    if(conn == null)
    {
      /*
       * * 创建一个HConnection
       * HConnection connection = HConnectionManager.createConnection(conf); 
       * HTableInterface table = connection.getTable("mytable");
       * table.get(...); ...
       * table.close(); 
       * connection.close();
       * */
      conn = HConnectionManager.createConnection(getConfiguration());
    }
    
    return conn;
  }
}

以上属于个人见解，如果有什么疑问和指教，欢迎指正。