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Date: Wed, 4 Jan 2012 23:54:39 +0000 (UTC)
From: "Todd Lipcon (Commented) (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-2751) Datanode drops OS cache behind reads
 even for short reads
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    [ https://issues.apache.org/jira/browse/HDFS-2751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13179997#comment-13179997 ] 

Todd Lipcon commented on HDFS-2751:
-----------------------------------

(thanks to JD Cryans for finding this one)
                
> 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
>
> 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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