HBase概念学习（九）HTablePool为什么弃用？

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

主题  HBase

咱们先看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，针对每一个线程建议都应该建立一个新的HTableInterface实例，这个建立过程是轻量的，缓存HTableInterface对象既不是必须的也不是推荐的！

而后再联想到只要HTable使用的Configuration是同一个，那么它们必定是共用一个HConnection的，HConnection才是HBase客户端到Hbase集群的真正的链接。

再想一想HTablePool的做用，无非就是HTable的链接池，里面维护的HTable应该来讲都是使用的同一个HConnecion。

既然HTable的建立是轻量级的，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！

因此Hbase抛弃了HTablePool，咱们惟一要作的就是保证HConnection实例是惟一的，全局共享的。而后针对HTableInterface对象最好在每次操做HBase表的时候根据HConnection对象来从新建立，使用完成以后及时关闭便可！

经过HConnection的getTable()方法就可以获取到用户操做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对象如何建立，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;   /**  * 获取全局惟一的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;  }   /**  * 获取全局惟一的HConnection实例  * @return  * @throws ZooKeeperConnectionException  */  public static synchronized HConnection getHConnection() throws ZooKeeperConnectionException  {   if(conn == null)   {    /*    * * 建立一个HConnection    * HConnection connection = HConnectionManager.createConnection(conf);    * HTableInterface table = connection.getTable("mytable");    * table.get(...); ...    * table.close();    * connection.close();    * */    conn = HConnectionManager.createConnection(getConfiguration());   }     return conn;  } }

以上属于我的看法，若是有什么疑问和指教，欢迎指正。