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https://issues.apache.org/jira/browse/HDFS-4656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13619436#comment-13619436
 ] 

Hadoop QA commented on HDFS-4656:
---------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest 
attachment 
  http://issues.apache.org/jira/secure/attachment/12576467/HDFS-4656.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author 
tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include 
any new or modified tests.
                        Please justify why no new tests are needed for this 
patch.
                        Also please list what manual steps were performed to 
verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the 
total number of javac compiler warnings.

    {color:green}+1 javadoc{color}.  The javadoc tool did not generate any 
warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with 
eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new 
Findbugs (version 1.3.9) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase 
the total number of release audit warnings.

    {color:red}-1 core tests{color}.  The patch failed these unit tests in 
hadoop-hdfs-project/hadoop-hdfs:

                  org.apache.hadoop.fs.TestFcHdfsSymlink

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: 
https://builds.apache.org/job/PreCommit-HDFS-Build/4176//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/4176//console

This message is automatically generated.
                
> 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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