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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4656) DN heartbeat loop can be briefly tight
Date Tue, 02 Apr 2013 02:05:16 GMT

    [ 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 
  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
                        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:


    {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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