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https://issues.apache.org/jira/browse/HADOOP-3524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12603822#action_12603822
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Brice Arnould commented on HADOOP-3524:
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Please excuse me, but I really don't think that it is a good idea.
The overall cost of having another thread to maintain would probably be greater
than just calling that function. In fact, even the access to the a field might
take more time than calling System.currentTimeMillis() (please refer to the
attached test). And even if it divided the cost of getting the current time by
100, that would probably have a negligible impact on performance, with the cost
of a greater complexity.
So I agree that there is many things to improve in the JobTracker, but not that.
(Please excuse me if I've been disrespectfull by inadvertance, I have
difficulties with English :-/)
> 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
>
> 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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