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Date: Thu, 11 Mar 2010 19:40:27 +0000 (UTC)
From: "ryan rawson (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-918) Use single Selector and small thread
 pool to replace many instances of BlockSender for reads
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    [ https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844195#action_12844195 ] 

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

this sounds great guys. For HBase, there is more need for the read path, rather than the write path.  I would love to test this for HBase, and we could postpone/delay the write path code.

> 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-918-20100211.patch, hdfs-918-20100228.patch, hdfs-918-20100309.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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