HBASE-4640 Catch ClosedChannelException and document it

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1245730 13f79535-47bb-0310-9956-ffa450edef68

src/docbkx/troubleshooting.xml

@@ -898,6 +898,15 @@ ERROR org.apache.hadoop.hbase.regionserver.HRegionServer: ZooKeeper session expi
                     symlink them into place and the message should go away.
                 </para>
         </section>
+        <section xml:id="trouble.rs.runtime.client_went_away">
+           <title>Server handler X on 60020 caught: java.nio.channels.ClosedChannelException</title>
+           <para>
+           If you see this type of message it means that the region server was trying to read/send data from/to a client but
+           it already went away. Typical causes for this are if the client was killed (you see a storm of messages like this when a MapReduce
+           job is killed or fails) or if the client receives a SocketTimeoutException. It's harmless, but you should consider digging in
+           a bit more if you aren't doing something to trigger them.
+           </para>
+        </section>
 
       </section>    
       <section xml:id="trouble.rs.shutdown">

src/main/java/org/apache/hadoop/hbase/ipc/HBaseServer.java

@@ -1378,6 +1378,11 @@ public abstract class HBaseServer implements RpcServer {
             // rethrow if no handler
             throw e;
           }
+       } catch (ClosedChannelException cce) {
+          LOG.warn(getName() + " caught a ClosedChannelException, " +
+            "this means that the server was processing a " +
+            "request but the client went away. The error message was: " +
+            cce.getMessage());
         } catch (Exception e) {
           LOG.warn(getName() + " caught: " +
                    StringUtils.stringifyException(e));