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https://issues.apache.org/jira/browse/HADOOP-3524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12603845#action_12603845
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Amar Kamat commented on HADOOP-3524:
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I ran Brice's test and following are the results
||num-iters||stale-time (ms)||accurate-time(ms)||
|1000|0| 2|
|10000| 1| 14|
|100000 |3| 126|
|1000000| 5| 1183|
|10000000| 30| 11675|
|100000000 |284| 117503|
This timer thread should be a simple _mostly-waiting_ thread. MR/JT scalability
is somewhat controlled by the heartbeat processing rate of the jobtracker. It
will be interesting to know what fraction of the heartbeat is taken up by the
call to {{System.currentTimeMillis()}}. BTW the timer solution was just a
starting point. I believe we can (if required) come up with a more simpler and
elegant solution.
> JobTracker's processHeartbeat() should not call System.currentTimeMillis()
> everytime
> ------------------------------------------------------------------------------------
>
> Key: HADOOP-3524
> URL: https://issues.apache.org/jira/browse/HADOOP-3524
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Amar Kamat
> Attachments: CurrentTimeCost.java
>
>
> Consider the following
> {code:title=JobTracker.java|borderStyle=solid}
> private synchronized boolean processHeartbeat(
> TaskTrackerStatus
> trackerStatus, boolean initialContact) {
> String trackerName = trackerStatus.getTrackerName();
> trackerStatus.setLastSeen(System.currentTimeMillis());
> {code}
> Here, the call to {{System.currentTimeMillis()}} on every call to
> {{JobTracker.processHeartbeat()}} might prove costly. While
> testing/benchmarking HADOOP-2119, we recorded that the JobTracker was able to
> serve ~130 tasks/sec. So that means we might make ~130 calls to
> {{System.currentTimeMillis()}} per second. I think in these cases
> (_last-seen-status_ etc) such a high level of accuracy in terms of timestamp
> is unnecessary and hence can be avoided.
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