[Hadoop Wiki] Update of "GangliaMetrics" by BrianBockelman

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The following page has been changed by BrianBockelman:
http://wiki.apache.org/hadoop/GangliaMetrics

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- Create a file called hadoop-metrics.properties, and stick it in your hadoop config directory.
+ Edit the file hadoop-metrics.properties, if it is not already present in your config directory.
  
- The file should look like this:
+ The file should contain at least the following lines:
  
  {{{
  dfs.class=org.apache.hadoop.metrics.ganglia.GangliaContext
  dfs.period=10
- dfs.servers=@GMETAD@:8650
+ dfs.servers=@GANGLIA@:8649
  
  mapred.class=org.apache.hadoop.metrics.ganglia.GangliaContext
  mapred.period=10
- mapred.servers=@GMETAD@:8650
+ mapred.servers=@GANGLIA@:8649
+ 
+ jvm.class=org.apache.hadoop.metrics.ganglia.GangliaContext
+ jvm.period=10
+ jvm.servers=@GANGLIA@:8649
  }}}
  
- I made hadoop talk directly to gmetad.  I found that if I have hadoop talk to gmond at localhost, then hadoop metrics get reported from 127.0.0.1, rather than from the more useful host name used to communicate with gmetad.
+ Replace @GANGLIA@ with the hostname or IP of the ganglia endpoint.  Depending on your Ganglia configuration, the host or IP you use might be:
+   * The value in the udp_send_channel you use in your /etc/gmond.conf (look for the line which says mcast_join=<IP ADDRESS>).
+   * The gmetad server
+   * Localhost
  
+ Be aware that versions 0.18.1 and prior need to be patched in order to get Ganglia working; refer to [https://issues.apache.org/jira/browse/HADOOP-3422 JIRA issue 3422].
+