org.apache.hadoop.hbase.client
Class HConnectionManager

java.lang.Object
  extended by org.apache.hadoop.hbase.client.HConnectionManager

public class HConnectionManager
extends Object

A non-instantiable class that manages HConnections. This class has a static Map of HConnection instances keyed by Configuration; all invocations of getConnection(Configuration) that pass the same Configuration instance will be returned the same HConnection instance (Adding properties to a Configuration instance does not change its object identity). Sharing HConnection instances is usually what you want; all clients of the HConnection instances share the HConnections' cache of Region locations rather than each having to discover for itself the location of meta, root, etc. It makes sense for the likes of the pool of HTables class HTablePool, for instance (If concerned that a single HConnection is insufficient for sharing amongst clients in say an heavily-multithreaded environment, in practise its not proven to be an issue. Besides, HConnection is implemented atop Hadoop RPC and as of this writing, Hadoop RPC does a connection per cluster-member, exclusively).

But sharing connections makes clean up of HConnection instances a little awkward. Currently, clients cleanup by calling deleteConnection(Configuration, boolean). This will shutdown the zookeeper connection the HConnection was using and clean up all HConnection resources as well as stopping proxies to servers out on the cluster. Not running the cleanup will not end the world; it'll just stall the closeup some and spew some zookeeper connection failed messages into the log. Running the cleanup on a HConnection that is subsequently used by another will cause breakage so be careful running cleanup.

To create a HConnection that is not shared by others, you can create a new Configuration instance, pass this new instance to getConnection(Configuration), and then when done, close it up by doing something like the following:

 Configuration newConfig = new Configuration(originalConf);
 HConnection connection = HConnectionManager.getConnection(newConfig);
 // Use the connection to your hearts' delight and then when done...
 HConnectionManager.deleteConnection(newConfig, true);
 
 

Cleanup used to be done inside in a shutdown hook. On startup we'd register a shutdown hook that called deleteAllConnections(boolean) on its way out but the order in which shutdown hooks run is not defined so were problematic for clients of HConnection that wanted to register their own shutdown hooks so we removed ours though this shifts the onus for cleanup to the client.


Constructor Summary
protected HConnectionManager()
           
 
Method Summary
static void deleteAllConnections(boolean stopProxy)
          Delete information for all connections.
static void deleteConnection(org.apache.hadoop.conf.Configuration conf, boolean stopProxy)
          Delete connection information for the instance specified by configuration.
static HConnection getConnection(org.apache.hadoop.conf.Configuration conf)
          Get the connection that goes with the passed conf configuration instance.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

HConnectionManager

protected HConnectionManager()
Method Detail

getConnection

public static HConnection getConnection(org.apache.hadoop.conf.Configuration conf)
                                 throws ZooKeeperConnectionException
Get the connection that goes with the passed conf configuration instance. If no current connection exists, method creates a new connection for the passed conf instance.

Parameters:
conf - configuration
Returns:
HConnection object for conf
Throws:
ZooKeeperConnectionException

deleteConnection

public static void deleteConnection(org.apache.hadoop.conf.Configuration conf,
                                    boolean stopProxy)
Delete connection information for the instance specified by configuration. This will close connection to the zookeeper ensemble and let go of all resources.

Parameters:
conf - configuration whose identity is used to find HConnection instance.
stopProxy - Shuts down all the proxy's put up to cluster members including to cluster HMaster. Calls HBaseRPC.stopProxy(org.apache.hadoop.ipc.VersionedProtocol).

deleteAllConnections

public static void deleteAllConnections(boolean stopProxy)
Delete information for all connections.

Parameters:
stopProxy - stop the proxy as well
Throws:
IOException


Copyright © 2011 The Apache Software Foundation. All Rights Reserved.