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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4418) HDFS-347: increase default FileInputStreamCache size
Date Thu, 17 Jan 2013 19:28:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13556503#comment-13556503
] 

Colin Patrick McCabe commented on HDFS-4418:
--------------------------------------------

looks reasonable to me; thanks, Todd.
                
> HDFS-347: increase default FileInputStreamCache size
> ----------------------------------------------------
>
>                 Key: HDFS-4418
>                 URL: https://issues.apache.org/jira/browse/HDFS-4418
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode, hdfs-client, performance
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-4418.txt
>
>
> The FileInputStreamCache currently defaults to holding only 10 input stream pairs (corresponding
to 10 blocks). In many HBase workloads, the region server will be issuing random reads against
a local file which is 2-4GB in size or even larger (hence 20+ blocks).
> Given that the memory usage for caching these input streams is low, and applications
like HBase tend to already increase their ulimit -n substantially (eg up to 32,000), I think
we should raise the default cache size to 50 or more. In the rare case that someone has an
application which uses local reads with hundreds of open blocks and can't feasibly raise their
ulimit -n, they can lower the limit appropriately.

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