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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4049) hflush performance regression due to nagling delays
Date Mon, 15 Oct 2012 19:47:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13476365#comment-13476365
] 

Todd Lipcon commented on HDFS-4049:
-----------------------------------

BTW, the latency readout in the benchmark currently isn't very useful since SampleQuantiles
doesn't have a toString(). I hacked it locally for the purposes of running the test, and just
filed HADOOP-8929 to actually get that into the code.
                
> 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: 3.0.0, 2.0.2-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>         Attachments: hdfs-4049.txt, hdfs-4049.txt
>
>
> 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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