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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