Todd Lipcon created HDFS-4049:
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             Summary: hflush performance regression due to nagling delays
                 Key: HDFS-4049
                 URL: https://issues.apache.org/jira/browse/HDFS-4049
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: data-node, performance
    Affects Versions: 2.0.2-alpha, 3.0.0
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon
            Priority: Critical


HDFS-3721 reworked the way that packets are mirrored through the pipeline in 
the datanode. This caused two write() calls where there used to be one, which 
interacts badly with nagling so that there are 40ms bubbles on hflush() calls. 
We didn't notice this in the tests because the hflush perf test only uses a 
single datanode.

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