[jira] Created: (MAPREDUCE-2116) optimize getTasksToKill to reduce JobTracker contention

["Joydeep Sen Sarma (JIRA)" <ji...@apache.org>]

optimize getTasksToKill to reduce JobTracker contention
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                 Key: MAPREDUCE-2116
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2116
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: jobtracker
            Reporter: Joydeep Sen Sarma


getTasksToKill shows up as one of the top routines holding the JT lock. Specifically, the translation from attemptid to tip is very expensive:

        at java.util.TreeMap.getEntry(TreeMap.java:328)
        at java.util.TreeMap.get(TreeMap.java:255)
        at org.apache.hadoop.mapred.TaskInProgress.shouldClose(TaskInProgress.java:500)
        at org.apache.hadoop.mapred.JobTracker.getTasksToKill(JobTracker.java:3464)
        - locked <0x00002aab6ebb6640> (a org.apache.hadoop.mapred.JobTracker)
        at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:3181)


this seems like an avoidable expense since the tip for a given attempt is fixed (and one should not need a map lookup to find the association). on a different note - not clear to me why TreeMaps are in use here (i didn't find any iteration over these maps). any background info on why things are arranged the way they are would be useful.

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