HADOOP-13667. Fix typing mistake of inline document in hadoop-metrics2.properties (Contributed by Rui Gao via Daniel Templeton)

hadoop-common-project/hadoop-common/src/main/conf/hadoop-metrics2.properties

@@ -50,9 +50,25 @@
 # If '*' all tags are used. If specifiying multiple tags separate them with 
 # commas. Note that the last segment of the property name is the context name.
 #
-#*.sink.ganglia.tagsForPrefix.jvm=ProcesName
-#*.sink.ganglia.tagsForPrefix.dfs=
-#*.sink.ganglia.tagsForPrefix.rpc=
+# A typical use of tags is separating the metrics by the HDFS rpc port
+# and HDFS service rpc port.
+# For example:
+#   With following HDFS configuration:
+#       dfs.namenode.rpc-address is set as namenodeAddress:9110
+#       dfs.namenode.servicerpc-address is set as namenodeAddress:9111
+#   If no tags are used, following metric would be gathered:
+#       rpc.rpc.NumOpenConnections
+#   If using "*.sink.ganglia.tagsForPrefix.rpc=port",
+#   following metrics would be gathered:
+#       rpc.rpc.port=9110.NumOpenConnections
+#       rpc.rpc.port=9111.NumOpenConnections
+#
+#*.sink.ganglia.tagsForPrefix.jvm=ProcessName
+#*.sink.ganglia.tagsForPrefix.dfs=HAState,IsOutOfSync
+#*.sink.ganglia.tagsForPrefix.rpc=port
+#*.sink.ganglia.tagsForPrefix.rpcdetailed=port
+#*.sink.ganglia.tagsForPrefix.metricssystem=*
+#*.sink.ganglia.tagsForPrefix.ugi=*
 #*.sink.ganglia.tagsForPrefix.mapred=
 
 #namenode.sink.ganglia.servers=yourgangliahost_1:8649,yourgangliahost_2:8649