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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-918) Use single Selector and small thread pool to replace many instances of BlockSender for reads
Date Tue, 09 Feb 2010 22:10:28 GMT

    [ https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12831696#action_12831696
] 

ryan rawson commented on HDFS-918:
----------------------------------

Great work, but Todd is dead on, we need to look at the few hundred but small chunk read scenario.
 It's currently where we hurt badly, and one of the things hopefully this patch can address.
I would be happy to test this out when you are ready.

> Use single Selector and small thread pool to replace many instances of BlockSender for
reads
> --------------------------------------------------------------------------------------------
>
>                 Key: HDFS-918
>                 URL: https://issues.apache.org/jira/browse/HDFS-918
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>            Reporter: Jay Booth
>             Fix For: 0.22.0
>
>         Attachments: hdfs-918-20100201.patch, hdfs-918-20100203.patch, hdfs-multiplex.patch
>
>
> Currently, on read requests, the DataXCeiver server allocates a new thread per request,
which must allocate its own buffers and leads to higher-than-optimal CPU and memory usage
by the sending threads.  If we had a single selector and a small threadpool to multiplex request
packets, we could theoretically achieve higher performance while taking up fewer resources
and leaving more CPU on datanodes available for mapred, hbase or whatever.  This can be done
without changing any wire protocols.

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