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https://issues.apache.org/jira/browse/MAPREDUCE-2116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920109#action_12920109
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Joydeep Sen Sarma commented on MAPREDUCE-2116:
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yeah - we are running with a patch that switches from TreeMap to HashMap (for
the tracker->attempt map) and keeps a pair of (attempt, tip) in the map. we
haven't deployed this on the main cluster yet - so can't say for certain how
much this will help. i can upload a patch for trunk later this week.
> optimize getTasksToKill to reduce JobTracker contention
> -------------------------------------------------------
>
> 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
> Attachments: getTaskToKill.JPG
>
>
> 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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