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Posted to common-dev@hadoop.apache.org by "Zheng Shao (JIRA)" <ji...@apache.org> on 2008/05/12 20:32:55 UTC
[jira] Assigned: (HADOOP-3370) failed tasks may stay forever in
TaskTracker.runningJobs
[ https://issues.apache.org/jira/browse/HADOOP-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Zheng Shao reassigned HADOOP-3370:
----------------------------------
Assignee: Zheng Shao
> failed tasks may stay forever in TaskTracker.runningJobs
> --------------------------------------------------------
>
> Key: HADOOP-3370
> URL: https://issues.apache.org/jira/browse/HADOOP-3370
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Priority: Critical
> Attachments: 3370-1.patch
>
>
> The net effect of this is that, with a long-running TaskTracker, it takes long long time for ReduceTasks on that TaskTracker to fetch map outputs - TaskTracker does that for all reduce tasks in TaskTracker .runningJobs, including those stale ReduceTasks. There is a 5-second delay between 2 requests, which makes it a long time for a running reducetask to get the map output locations, when there are tens of stale ReduceTasks. Of course this also blows up the memory but that is not a too big problem at its rate.
> I've verified the bug by adding an html table for TaskTracker.runningJobs on TaskTracker http interface, on a 2-node machine, with a single mapper single reducer job, in which mapper succeeds and reducer fails. I can still see the ReduceTask in TaskTracker.runningJobs, while it's not in the first 2 tables (TaskTracker.tasks and TaskTracker.runningTasks).
> Details:
> TaskRunner.run() will call TaskTracker.reportTaskFinished() when the task fails,
> which calls TaskTracker.TaskInProgress.taskFinished,
> which calls TaskTracker.TaskInProgress.cleanup(),
> which calls TaskTracker.tasks.remove(taskId).
> In short, it remove a failed task from TaskTracker.tasks, but not TaskTracker.runningJobs.
> Then the failure is reported to JobTracker.
> JobTracker.heartbeat will call processHeartbeat,
> which calls updateTaskStatuses,
> which calls tip.getJob().updateTaskStatus,
> which calls JobInProgress.failedTask,
> which calls JobTracker.markCompletedTaskAttempt,
> which puts the task to trackerToMarkedTasksMap,
> and then JobTracker.heartbeat will call removeMarkedTasks,
> which call removeTaskEntry,
> which removes it from trackerToTaskMap.
> JobTracker.heartbeat will also call JobTracker.getTasksToKill,
> which reads from trackerToTaskMap for <tracker, task> pairs,
> and ask tracker to KILL the task or job of the task.
> In the case there is only one task for a specific job on a specific tracker
> and that task failed (NOTE: and that task is not the last failed try of the
> job - otherwise JobTracker.getTasksToKill will pick it up before
> removeMarkedTasks comes in and remove it from trackerToTaskMap), the task
> tracker will not receive the KILL task or KILL job message from the JobTracker.
> As a result, the task will remain in TaskTracker.runningJobs forever.
> Solution:
> Remove the task from TaskTracker.runningJobs at the same time when we remove it from TaskTracker.tasks.
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