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https://issues.apache.org/jira/browse/MAPREDUCE-4728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13582571#comment-13582571
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Thomas Graves commented on MAPREDUCE-4728:
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this might be a dup of MAPREDUCE-4478
> Interaction between oob heartbeats and damper can cause TT to heartbeat with
> zero delay
> ---------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4728
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4728
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 1.0.3
> Reporter: Nathan Roberts
> Attachments: MAPREDUCE-4728.patch
>
>
> When mapreduce.tasktracker.outofband.heartbeat is true and
> mapreduce.tasktracker.outofband.heartbeat.damper is something largish (like
> the default of 1000000), the TT doesn't wait for tasks to finish before
> heartbeating back to the JT. This causes excessive load on the JT which
> in-turn reduces overall cluster performance.
> I believe the problem is that in the following block of code, when
> getHeartbeatInterval() returns 0, we heartbeat back immediately BUT
> finishedCount does not get reset. It looks like nothing ever gets us out of
> this situation so we basically heartbeat without ever sleeping.
>
> {code}
> // accelerate to account for multiple finished tasks up-front
> long remaining =
> (lastHeartbeat + getHeartbeatInterval(finishedCount.get())) - now;
> while (remaining > 0) {
> // sleeps for the wait time or
> // until there are *enough* empty slots to schedule tasks
> synchronized (finishedCount) {
> finishedCount.wait(remaining);
> // Recompute
> now = System.currentTimeMillis();
> remaining =
> (lastHeartbeat + getHeartbeatInterval(finishedCount.get())) -
> now;
> if (remaining <= 0) {
> // Reset count
> finishedCount.set(0);
> break;
> }
> }
> }
> {code}
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