Major Description
Today, we see that a TaskTracer has keeped throwing the same exception in our production environment.it is that:
2013-07-01 18:41:40,023 INFO org.apache.hadoop.mapred.TaskTracker: addFreeSlot : current free slots : 7
2013-07-01 18:41:43,026 INFO org.apache.hadoop.mapred.TaskTracker: LaunchTaskAction (registerTask): attempt_201208241212_27521_m_000002_3 task's state:UNASSIGNED
2013-07-01 18:41:43,026 INFO org.apache.hadoop.mapred.TaskTracker: Trying to launch : attempt_201208241212_27521_m_000002_3 which needs 1 slots
2013-07-01 18:41:43,026 INFO org.apache.hadoop.mapred.TaskTracker: In TaskLauncher, current free slots : 7 and trying to launch attempt_201208241212_27521_m_000002_3 which needs 1 slots
2013-07-01 18:41:43,026 INFO org.apache.hadoop.mapreduce.server.tasktracker.Localizer: User-directories for the user sds are already initialized on this TT. Not doing anything.
2013-07-01 18:41:43,029 WARN org.apache.hadoop.mapred.TaskTracker: Error initializing attempt_201208241212_27521_m_000002_3:
java.lang.NullPointerException
2013-07-01 18:41:43,029 ERROR org.apache.hadoop.mapred.TaskStatus: Trying to set finish time for task attempt_201208241212_27521_m_000002_3 when no start time is set, stackTrace is : java.lang.Exception
at org.apache.hadoop.mapred.TaskStatus.setFinishTime(TaskStatus.java:195)
at org.apache.hadoop.mapred.MapTaskStatus.setFinishTime(MapTaskStatus.java:51)
at org.apache.hadoop.mapred.TaskTracker$TaskInProgress.kill(TaskTracker.java:2937)
at org.apache.hadoop.mapred.TaskTracker.startNewTask(TaskTracker.java:2255)
at org.apache.hadoop.mapred.TaskTracker$TaskLauncher.run(TaskTracker.java:2212)
Then, we view the log files of the TaskTracker,and find that the TaskTracker throwed Several OutOfMemoryError: Java heap space about ten days ago. after that, the TaskTracker has still throws the exception:
2013-06-22 12:39:42,296 INFO org.apache.hadoop.mapred.TaskTracker: LaunchTaskAction (registerTask): attempt_201208241212_26088_m_000043_1 task's state:UNASSIGNED
2013-06-22 12:39:42,296 INFO org.apache.hadoop.mapred.TaskTracker: Trying to launch : attempt_201208241212_26088_m_000043_1 which needs 1 slots
2013-06-22 12:39:42,296 INFO org.apache.hadoop.mapred.TaskTracker: In TaskLauncher, current free slots : 7 and trying to launch attempt_201208241212_26088_m_000043_1 which needs 1 slots
2013-06-22 12:39:42,296 INFO org.apache.hadoop.mapreduce.server.tasktracker.Localizer: Initializing user sds on this TT.
2013-06-22 12:39:42,300 WARN org.apache.hadoop.mapred.TaskTracker: Error initializing attempt_201208241212_26088_m_000043_1:
java.lang.NullPointerException
at org.apache.hadoop.ipc.Client$Connection.sendParam(Client.java:630)
at org.apache.hadoop.ipc.Client.call(Client.java:886)
at org.apache.hadoop.ipc.WritableRpcEngine$Invoker.invoke(WritableRpcEngine.java:198)
at $Proxy5.getFileInfo(Unknown Source)
at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy5.getFileInfo(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient.getFileInfo(DFSClient.java:850)
at org.apache.hadoop.hdfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:620)
at org.apache.hadoop.mapred.TaskTracker.localizeJobTokenFile(TaskTracker.java:3984)
at org.apache.hadoop.mapred.TaskTracker.localizeJobFiles(TaskTracker.java:1036)
at org.apache.hadoop.mapred.TaskTracker.localizeJob(TaskTracker.java:977)
at org.apache.hadoop.mapred.TaskTracker.startNewTask(TaskTracker.java:2247)
at org.apache.hadoop.mapred.TaskTracker$TaskLauncher.run(TaskTracker.java:2212)
2013-06-22 12:39:42,300 ERROR org.apache.hadoop.mapred.TaskStatus: Trying to set finish time for task attempt_201208241212_26088_m_000043_1 when no start time is set, stackTrace is : java.lang.Exception
at org.apache.hadoop.mapred.TaskStatus.setFinishTime(TaskStatus.java:195)
at org.apache.hadoop.mapred.MapTaskStatus.setFinishTime(MapTaskStatus.java:51)
at org.apache.hadoop.mapred.TaskTracker$TaskInProgress.kill(TaskTracker.java:2937)
at org.apache.hadoop.mapred.TaskTracker.startNewTask(TaskTracker.java:2255)
at org.apache.hadoop.mapred.TaskTracker$TaskLauncher.run(TaskTracker.java:2212)
Since then, the TaskTracker has not completed any task.we can find the property of Connection -out is null from the above exeption,and it is caused by the failure of method setupIOstream() in the class org.apache.ipc.Client$Connection.anyway, the instance of Connection is not null and cached by the org.apache.ipc.Client.
private Connection getConnection(InetSocketAddress addr, Class<?> protocol, UserGroupInformation ticket, Call call) throws IOException, InterruptedException { if (!running.get()) { // the client is stopped throw new IOException("The client is stopped"); } Connection connection; /* we could avoid this allocation for each RPC by having a * connectionsId object and with set() method. We need to manage the * refs for keys in HashMap properly. For now its ok. */ ConnectionId remoteId = new ConnectionId(addr, protocol, ticket); do { synchronized (connections) { connection = connections.get(remoteId); if (connection == null) { connection = new Connection(remoteId); connections.put(remoteId, connection); } } } while (!connection.addCall(call)); //we don't invoke the method below inside "synchronized (connections)" //block above. The reason for that is if the server happens to be slow, //it will take longer to establish a connection and that will slow the //entire system down. connection.setupIOstreams(); return connection; }
We guess that it throwed a OutOfMemoryError when a thread called the setupIOstream() because of RPC, so that some properties of the Connection are null, and throw NullPointerException when the Connection are accessed by other threads,which is fron the cache.It must be correct to make sure that the instance of Connection could only be access after initialized successfully.
On the other hand, we also simulate this scenario.Firstly, one thread create the Connection instance and throw OutOfMemoryError when it call connection.setupIOstreams().after that, the other thread start call RPC through by the instance and it keeps throwing the same exceptions