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Date: Wed, 10 Feb 2010 08:54:27 +0000 (UTC)
From: "Amareshwari Sriramadasu (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Created: (MAPREDUCE-1475) Race condition while launching
 task cleanup attempt.
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Race condition while launching task cleanup attempt.
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                 Key: MAPREDUCE-1475
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1475
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: tasktracker
    Affects Versions: 0.20.1
            Reporter: Amareshwari Sriramadasu


We found a race condition while launching task cleanup attempt on a TaskTracker which would eat up a slot.

The scenario is the following:
The main attempt is killed by TaskTracker because it was a speculative attempt. Cleanup attempt is launched on the same tracker. Cleanup attempt occupied the slot and is about to start. But, there was a pending RPC: done() from earlier attempt in the RPC queue. Before the cleanup attempt could be launched, TaskTracker processed the rpc from earlier attempt and made the state of the cleanup attempt as KILLED. Launcher did not launch it because it was already KILLED. But, the rpc done() failed with NullPointerException because of false state. In summary, the slot was occupied by the cleanup attempt which could not be launched. And the slot was never released.


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