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From "Todd Lipcon (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 Thu, 11 Mar 2010 20:00:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844208#action_12844208
] 

Todd Lipcon commented on HDFS-918:
----------------------------------

+1 on ignoring write for now. This mainly benefits high concurrency random reads, let's get
this working and then think about the write path.

I can devote some time to benchmarking and reviewing this more thoroughly, but likely not
until the end of this month / beginning of next.

> 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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