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https://issues.apache.org/jira/browse/HDFS-4656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13619446#comment-13619446
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Aaron T. Myers commented on HDFS-4656:
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Thanks a lot for the review, Todd.
The test failure is unrelated and is already tracked by another JIRA. I'm going
to commit this momentarily.
> DN heartbeat loop can be briefly tight
> --------------------------------------
>
> Key: HDFS-4656
> URL: https://issues.apache.org/jira/browse/HDFS-4656
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 2.0.4-alpha
> Reporter: Aaron T. Myers
> Assignee: Aaron T. Myers
> Priority: Minor
> Attachments: HDFS-4656.patch
>
>
> The DN hearbeat loop looks roughly like this:
> {code}
> if (now - timeOfLastHeartbeat > configuredHeartbeatInterval) {
> // do heartbeat
> }
> timeToWait = configuredHeartbeatInterval - (now - timeOfLastHeartbeat)
> sleep(timeToWait)
> {code}
> The trouble is that since we sleep for exactly the heartbeat interval, and
> then check to see if we have waited _more_ than that heartbeat interval, we
> will very often have waited exactly the heartbeat interval (in millis), and
> not more than it. In this case we will skip actually performing the heartbeat
> and will calculcate timeToWait as being 0ms. The DN heartbeat loop will then
> loop tightly for 1ms. The solution is just to change the "{{>}}" in the code
> above to "{{>=}}".
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