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From "Scott Chen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-2116) optimize getTasksToKill to reduce JobTracker contention
Date Tue, 12 Oct 2010 18:37:34 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920293#action_12920293
] 

Scott Chen commented on MAPREDUCE-2116:
---------------------------------------

Hey louli,
That's a nice observation. Nice graph too.
bq. what if we keep a ref in TaskAttemptID class to point to its TIP ref?
Joydeep has similar idea. But he created another class that keeps a pair. We are testing this
internally.

> 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: 2116.1.patch, 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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