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HBASE-11518 doc update for how to create non-shared HConnection (Qiang Tian)

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stack 2014-07-17 11:39:00 -07:00
parent d6c5e5f374
commit f8153a1456
1 changed files with 17 additions and 23 deletions
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40
hbase-client/src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
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@ -44,24 +44,18 @@ import org.apache.hadoop.hbase.security.User;
* connection.close();
* }
* }</pre>
* <p>The following logic and API will be removed in the future:
* <p>This class has a static Map of {@link HConnection} instances keyed by
* {@link Configuration}; all invocations of {@link #getConnection(Configuration)}
* that pass the same {@link Configuration} instance will be returned the same
* {@link HConnection} instance (Adding properties to a Configuration
* instance does not change its object identity; for more on how this is done see
* {@link HConnectionKey}). Sharing {@link HConnection}
* instances is usually what you want; all clients of the {@link HConnection}
* instances share the HConnections' cache of Region locations rather than each
* having to discover for itself the location of meta, etc. It makes
* sense for the likes of the pool of HTables class {@link HTablePool}, for
* instance (If concerned that a single {@link HConnection} is insufficient
* for sharing amongst clients in say an heavily-multithreaded environment,
* in practise its not proven to be an issue. Besides, {@link HConnection} is
* implemented atop Hadoop RPC and as of this writing, Hadoop RPC does a
* connection per cluster-member, exclusively).
*
* <p>But sharing connections makes clean up of {@link HConnection} instances a little awkward.
* {@link HConnectionKey}; A {@link HConnectionKey} is identified by a set of
* {@link Configuration} properties. Invocations of {@link #getConnection(Configuration)}
* that pass the same {@link Configuration} instance will return the same
* {@link HConnection} instance ONLY WHEN the set of properties are the same
* (i.e. if you change properties in your {@link Configuration} instance, such as RPC timeout,
* the codec used, HBase will create a new {@link HConnection} instance. For more details on
* how this is done see {@link HConnectionKey}).
* <p>Sharing {@link HConnection} instances is usually what you want; all clients
* of the {@link HConnection} instances share the HConnections' cache of Region
* locations rather than each having to discover for itself the location of meta, etc.
* But sharing connections makes clean up of {@link HConnection} instances a little awkward.
* Currently, clients cleanup by calling {@link #deleteConnection(Configuration)}. 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
@ -71,15 +65,15 @@ import org.apache.hadoop.hbase.security.User;
* subsequently used by another will cause breakage so be careful running
* cleanup.
* <p>To create a {@link HConnection} that is not shared by others, you can
* create a new {@link Configuration} instance, pass this new instance to
* {@link #getConnection(Configuration)}, and then when done, close it up by
* doing something like the following:
* set property "hbase.client.instance.id" to a unique value for your {@link Configuration}
* instance, like the following:
* <pre>
* {@code
* Configuration newConfig = new Configuration(originalConf);
* HConnection connection = HConnectionManager.getConnection(newConfig);
* conf.set("hbase.client.instance.id", "12345");
* HConnection connection = HConnectionManager.getConnection(conf);
* // Use the connection to your hearts' delight and then when done...
* HConnectionManager.deleteConnection(newConfig, true);
* conf.set("hbase.client.instance.id", "12345");
* HConnectionManager.deleteConnection(conf, true);
* }
* </pre>
* <p>Cleanup used to be done inside in a shutdown hook. On startup we'd