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https://issues.apache.org/jira/browse/HDFS-2751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13420954#comment-13420954
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Brandon Li commented on HDFS-2751:
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Uploaded patch to back port to branch-1.
> 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.branch-1.patch, 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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