Nate Putnam created HADOOP-9128:
-----------------------------------

             Summary: MetricsDynamicMBeanBase can cause high cpu load
                 Key: HADOOP-9128
                 URL: https://issues.apache.org/jira/browse/HADOOP-9128
             Project: Hadoop Common
          Issue Type: Bug
          Components: metrics
    Affects Versions: 0.20.2
         Environment: cdh3u4
            Reporter: Nate Putnam


I noticed high load on some of our Hadoop services. On closer inspection we 
found several threads that were consuming cpu (80-90% of a core) doing : 

java.lang.Thread.State: RUNNABLE
at java.util.HashMap.get(HashMap.java:303)
at 
org.apache.hadoop.metrics.util.MetricsDynamicMBeanBase.getAttribute(MetricsDynamicMBeanBase.java:135)
at 
com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.getAttribute(DefaultMBeanServerInterceptor.java:666)

This is a known issue in java when using a non thread safe hash map from 
multiple threads. 

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