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[数据库]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。