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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2114) user finer grained locks in JT getCounters implementation
Date Thu, 07 Oct 2010 00:53:31 GMT
user finer grained locks in JT getCounters implementation
---------------------------------------------------------

                 Key: MAPREDUCE-2114
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2114
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: jobtracker
            Reporter: Joydeep Sen Sarma


We are bound on the JobTracker lock on our largest cluster. One pattern i have seen is the
following:

- JT acquires JobTracker lock - but blocked on JIP lock:

java.lang.Thread.State: BLOCKED (on object monitor)
at org.apache.hadoop.mapred.JobInProgress.updateTaskStatus(JobInProgress.java:1028)
- waiting to lock <0x00002aae21092ff8> (a org.apache.hadoop.mapred.JobInProgress)
at org.apache.hadoop.mapred.JobTracker.updateTaskStatuses(JobTracker.java:4403)
at org.apache.hadoop.mapred.JobTracker.processHeartbeat(JobTracker.java:3444)
- locked <0x00002aab6ebb6640> (a org.apache.hadoop.mapred.JobTracker)

- the JIP lock is typically held by a getcounters call:

- locked <0x00002aaaf88beff8> (a org.apache.hadoop.mapred.Counters$Group)
at org.apache.hadoop.mapred.Counters.incrAllCounters(Counters.java:445)
- locked <0x00002aaaf88bb948> (a org.apache.hadoop.mapred.Counters)
at org.apache.hadoop.mapred.JobInProgress.incrementTaskCounters(JobInProgress.java:1253)
at org.apache.hadoop.mapred.JobInProgress.getCounters(JobInProgress.java:1240)
- locked <0x00002aae21092ff8> (a org.apache.hadoop.mapred.JobInProgress)

the solution seems simple. in order to summarize the counters for all tasks - we need to only
lock one task's counters at a time. we don't need to lock the entire job. 

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