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From "Hudson (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2751) Datanode drops OS cache behind reads even for short reads
Date Fri, 20 Jan 2012 07:43:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13189670#comment-13189670

Hudson commented on HDFS-2751:

Integrated in Hadoop-Common-0.23-Commit #392 (See [https://builds.apache.org/job/Hadoop-Common-0.23-Commit/392/])
    HDFS-2751. Datanode may incorrectly drop OS cache behind reads even for short reads. Contributed
by Todd Lipcon.

todd : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1233795
Files : 
* /hadoop/common/branches/branch-0.23/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
* /hadoop/common/branches/branch-0.23/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockSender.java

> Datanode drops OS cache behind reads even for short reads
> ---------------------------------------------------------
>                 Key: HDFS-2751
>                 URL: https://issues.apache.org/jira/browse/HDFS-2751
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.23.0, 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.24.0, 0.23.1
>         Attachments: hdfs-2751.txt, hdfs-2751.txt
> HDFS-2465 has some code which attempts to disable the "drop cache behind reads" functionality
when the reads are <256KB (eg HBase random access). But this check was missing in the {{close()}}
function, so it always drops cache behind reads regardless of the size of the read. This hurts
HBase random read performance when this patch is enabled.

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