HBase概念學習（九）HTablePool爲什麼棄用？

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

主題  HBase

咱們先看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

上面說HTable的的父類HTableInterface是非線程安全的，針對每一個線程建議都應該建立一個新的HTableInterface實例，這個建立過程是輕量的，緩存HTableInterface對象既不是必須的也不是推薦的！

而後再聯想到只要HTable使用的Configuration是同一個，那麼它們必定是共用一個HConnection的，HConnection纔是HBase客戶端到Hbase集羣的真正的鏈接。

再想一想HTablePool的做用，無非就是HTable的鏈接池，裏面維護的HTable應該來講都是使用的同一個HConnecion。

既然HTable的建立是輕量級的，使用同一個Confuguration的HTable都會共用一個HConnection，那麼HTablePool就顯得那麼多餘！

因此Hbase拋棄了HTablePool，咱們惟一要作的就是保證HConnection實例是惟一的，全局共享的。而後針對HTableInterface對象最好在每次操做HBase表的時候根據HConnection對象來從新建立，使用完成以後及時關閉便可！

經過HConnection的getTable()方法就可以獲取到用戶操做HBase表的HTableInterface對象了。

下面是一個使用HConnection的getTable()方法獲取HTableInterface對象的例子：

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");  }

至於HConnection對象如何建立，HBase推薦使用的方法是：

• 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

下面代碼是我按照單例模式維護HConnection對象的例子：

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;   /**  * 獲取全局惟一的Configuration實例  * @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;  }   /**  * 獲取全局惟一的HConnection實例  * @return  * @throws ZooKeeperConnectionException  */  public static synchronized HConnection getHConnection() throws ZooKeeperConnectionException  {   if(conn == null)   {    /*    * * 建立一個HConnection    * HConnection connection = HConnectionManager.createConnection(conf);    * HTableInterface table = connection.getTable("mytable");    * table.get(...); ...    * table.close();    * connection.close();    * */    conn = HConnectionManager.createConnection(getConfiguration());   }     return conn;  } }

以上屬於我的看法，若是有什麼疑問和指教，歡迎指正。