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Date: Thu, 9 Feb 2012 21:32:57 +0000 (UTC)
From: "Hadoop QA (Commented) (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HADOOP-8052) Hadoop Metrics2 should emit
 Float.MAX_VALUE (instead of Double.MAX_VALUE) to avoid making Ganglia's
 gmetad core
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    [ https://issues.apache.org/jira/browse/HADOOP-8052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13204897#comment-13204897 ] 

Hadoop QA commented on HADOOP-8052:
-----------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12514006/HADOOP-8052.patch
  against trunk revision .

    +1 @author.  The patch does not contain any @author tags.

    -1 tests included.  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.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 eclipse:eclipse.  The patch built with eclipse:eclipse.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit warnings.

    -1 core tests.  The patch failed these unit tests:
                  org.apache.hadoop.metrics2.util.TestSampleStat

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HADOOP-Build/582//testReport/
Console output: https://builds.apache.org/job/PreCommit-HADOOP-Build/582//console

This message is automatically generated.
                
> Hadoop Metrics2 should emit Float.MAX_VALUE (instead of Double.MAX_VALUE) to avoid making Ganglia's gmetad core
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-8052
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8052
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: metrics
>    Affects Versions: 0.23.0, 1.0.0
>            Reporter: Varun Kapoor
>            Assignee: Varun Kapoor
>              Labels: patch
>         Attachments: HADOOP-8052-branch-1.patch, HADOOP-8052.patch
>
>
> Ganglia's gmetad converts the doubles emitted by Hadoop's Metrics2 system to strings, and the buffer it uses is 256 bytes wide.
> When the SampleStat.MinMax class (in org.apache.hadoop.metrics2.util) emits its default min value (currently initialized to Double.MAX_VALUE), it ends up causing a buffer overflow in gmetad, which causes it to core, effectively rendering Ganglia useless (for some, the core is continuous; for others who are more fortunate, it's only a one-time Hadoop-startup-time thing).
> The fix needed to Ganglia is simple - the buffer needs to be bumped up to be 512 bytes wide, and all will be well - but instead of requiring a minimum version of Ganglia to work with Hadoop's Metrics2 system, it might be more prudent to just use Float.MAX_VALUE.
> An additional problem caused in librrd (which Ganglia uses beneath-the-covers) by the use of Double.MIN_VALUE (which functions as the default max value) is an underflow when librrd runs the received strings through libc's strtod(), but the librrd code is good enough to check for this, and only emits a warning - moving to Float.MIN_VALUE fixes that as well.

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