HADOOP-8118. In metrics2.util.MBeans, change log level to trace for the stack trace of InstanceAlreadyExistsException.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1295240 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -160,6 +160,9 @@ Release 0.23.3 - UNRELEASED
     HADOOP-8098. KerberosAuthenticatorHandler should use _HOST replacement to 
     resolve principal name (tucu)
 
+    HADOOP-8118.  In metrics2.util.MBeans, change log level to trace for the
+    stack trace of InstanceAlreadyExistsException.  (szetszwo)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/MBeans.java

@@ -18,6 +18,8 @@
 package org.apache.hadoop.metrics2.util;
 
 import java.lang.management.ManagementFactory;
+
+import javax.management.InstanceAlreadyExistsException;
 import javax.management.MBeanServer;
 import javax.management.ObjectName;
 
@@ -55,8 +57,15 @@ public class MBeans {
       mbs.registerMBean(theMbean, name);
       LOG.debug("Registered "+ name);
       return name;
+    } catch (InstanceAlreadyExistsException iaee) {
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("Failed to register MBean \""+ name + "\"", iaee);
+      } else {
+        LOG.warn("Failed to register MBean \""+ name
+            + "\": Instance already exists.");
+      }
     } catch (Exception e) {
-      LOG.warn("Error registering "+ name, e);
+      LOG.warn("Failed to register MBean \""+ name + "\"", e);
     }
     return null;
   }