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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-12533) NNThroughputBenchmark threads get stuck on UGI.getCurrentUser()
Date Fri, 22 Sep 2017 21:55:00 GMT
Erik Krogen created HDFS-12533:

             Summary: NNThroughputBenchmark threads get stuck on UGI.getCurrentUser()
                 Key: HDFS-12533
                 URL: https://issues.apache.org/jira/browse/HDFS-12533
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Erik Krogen

In {{NameNode#getRemoteUser()}}, it first attempts to fetch from the RPC user (not a synchronized
operation), and if there is no RPC call, it will call {{UserGroupInformation#getCurrentUser()}}
(which is {{synchronized}}). This makes it efficient for RPC operations (the bulk) so that
there is not too much contention.

In NNThroughputBenchmark, however, there is no RPC call since we bypass that later, so with
a high thread count many of the threads are getting stuck. At one point I attached a profiler
and found that quite a few threads had been waiting for {{#getCurrentUser()}} for 2 minutes
(!). When taking this away I found some improvement in the throughput numbers I was seeing.
To more closely emulate a real NN we should improve this issue.

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