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https://issues.apache.org/jira/browse/MAPREDUCE-4478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422022#comment-13422022
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Liyin Liang commented on MAPREDUCE-4478:
----------------------------------------
There are two configuration items to control the TaskTracker's heartbeat
interval. One is *mapreduce.tasktracker.outofband.heartbeat*. The other is
*mapreduce.tasktracker.outofband.heartbeat.damper*. If we set
*mapreduce.tasktracker.outofband.heartbeat* with true and set
*mapreduce.tasktracker.outofband.heartbeat.damper* with default value
(1000000), TaskTracker may send heartbeat without any interval.
The code to control heartbeat interval is as follows:
{code:java}
long now = System.currentTimeMillis();
// 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}
During the first time computing, if *finishedCount* is more than zero,
*getHeartbeatInterval(finishedCount.get())* will return zero. Then *remaining*
will be less than or equal with zero. In this case, the *while* loop will be
skipped. So *finishedCount* will never be set with zero.
> TaskTracker's heartbeat is out of control
> -----------------------------------------
>
> Key: MAPREDUCE-4478
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4478
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 1.0.0, 1.0.1, 1.0.2, 1.0.3
> Reporter: Liyin Liang
>
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