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From "Rajesh Balamohan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1495) Reduce locking contention on JobTracker.getTaskCompletionEvents()
Date Tue, 16 Feb 2010 00:20:27 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12834030#action_12834030
] 

Rajesh Balamohan commented on MAPREDUCE-1495:
---------------------------------------------

Made the following changes to reduce contentions and profiled JT. This virtually eliminated
the 
contentions caused by getTaskCompletionEvents 

In JobTracker.java: (locking only jobs during get())

  public TaskCompletionEvent[] getTaskCompletionEvents(
      JobID jobid, int fromEventId, int maxEvents) throws IOException{
    JobInProgress job = null;
    synchronized (jobs) {
      job = this.jobs.get(jobid);
    }
    if (null != job) {
      if (job.inited()) {
        return job.getTaskCompletionEvents(fromEventId, maxEvents);
      } else {
        return EMPTY_EVENTS;
      }
    }
    return completedJobStatusStore.readJobTaskCompletionEvents(jobid, fromEventId, maxEvents);
  }
  
In Configuration.java: (eliminated synchronize on  method level. This might be required only
when properties is null)
  private Properties getProps() {
    if (properties == null) {
      synchronized(this) {
        properties = new Properties();
        loadResources(properties, resources, quietmode);
        if (overlay!= null) {
          properties.putAll(overlay);
          if (storeResource) {
            for (Map.Entry<Object,Object> item: overlay.entrySet()) {
              updatingResource.put((String) item.getKey(), "Unknown");
            }
          }
        }
      }
	}
    return properties;
  }

> Reduce locking contention on JobTracker.getTaskCompletionEvents()
> -----------------------------------------------------------------
>
>                 Key: MAPREDUCE-1495
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1495
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>    Affects Versions: 0.20.1
>            Reporter: Rajesh Balamohan
>
> While profiling JT for slow performance with small-jobs, it was observed that JobTracker.getTaskCompletionEvents()
is attributing to 40% of lock contention on JT.
> This JIRA ticket is created to explore the possibilities of reducing the sychronized
code block in this method. 

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