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Javax.management.InstanceAlreadyExistsException when using hasoop MiniDFSCluster

I am using MiniDFSCluster to run junit tests. Now I just start and close the cluster, junit is working in green. But I get this exception:

javax.management.InstanceAlreadyExistsException: MXBean already registered with name Hadoop:service=NameNode,name=MetricsSystem,sub=Control at com.sun.jmx.mbeanserver.MXBeanLookup.addReference(MXBeanLookup.java:120) at com.sun.jmx.mbeanserver.MXBeanSupport.register(MXBeanSupport.java:143) at com.sun.jmx.mbeanserver.MBeanSupport.preRegister2(MBeanSupport.java:183) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerDynamicMBean(DefaultMBeanServerInterceptor.java:941) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerObject(DefaultMBeanServerInterceptor.java:917) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:312) at com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:482) at org.apache.hadoop.metrics2.util.MBeans.register(MBeans.java:56) at org.apache.hadoop.metrics2.impl.MetricsSystemImpl.initSystemMBean(MetricsSystemImpl.java:500) at org.apache.hadoop.metrics2.impl.MetricsSystemImpl.init(MetricsSystemImpl.java:140) at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.init(DefaultMetricsSystem.java:40) at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.initialize(DefaultMetricsSystem.java:50) at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1483) at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1459) at org.apache.hadoop.hdfs.MiniDFSCluster.startDataNodes(MiniDFSCluster.java:417) at org.apache.hadoop.hdfs.MiniDFSCluster.<init>(MiniDFSCluster.java:280) at org.apache.hadoop.hdfs.MiniDFSCluster.<init>(MiniDFSCluster.java:124) at com.myCompany.TestAll.testInit(TestAll.java:30) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at junit.framework.TestCase.runTest(TestCase.java:168) at junit.framework.TestCase.runBare(TestCase.java:134) at junit.framework.TestResult$1.protect(TestResult.java:110) at junit.framework.TestResult.runProtected(TestResult.java:128) at junit.framework.TestResult.run(TestResult.java:113) at junit.framework.TestCase.run(TestCase.java:124) at junit.framework.TestSuite.runTest(TestSuite.java:232) at junit.framework.TestSuite.run(TestSuite.java:227) at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Can someone please give me some suggestion about this exception?

Many thanks.

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2 answers

What happens is that hadoop registers the jmx bean for monitoring. At the first start of hasoop, it registers a bean, but the second time the hasoop starts, a bean with this name is already registered, which leads to the error above.

Either you do not close MiniDFSCluster correctly, or you start it more than once, or an error appears in MiniDFSCluster, because of which it does not clean up properly.

You call cluster.shutdown() in the teardown method, as shown here .

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Even if you cause shutdown, you still get an error as long as https://issues.apache.org/jira/browse/HBASE-4709 is allowed

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