hadoop-common-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Varun Kapoor (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-8052) Hadoop Metrics2 should emit Float.MAX_VALUE (instead of Double.MAX_VALUE) to avoid making Ganglia's gmetad core
Date Thu, 09 Feb 2012 20:58:58 GMT
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: 1.0.0, 0.23.0
            Reporter: Varun Kapoor
            Assignee: Varun Kapoor


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.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira

        

Mime
View raw message