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https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12893807#action_12893807
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Jean-Daniel Cryans commented on HDFS-918:
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I tested the latest full patch (not the pool one) and didn't see any issue, 
although it was on a single machine and with block cache ON (but lots of 
evictions). I need to do some more proper testing on my test cluster.

bq. Would people be interested in another JIRA focusing on just the pooling 
improvements

I am, and I think that having smaller patches will help getting this committed.

> 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: hbase-hdfs-benchmarks.ods, hdfs-918-20100201.patch, 
> hdfs-918-20100203.patch, hdfs-918-20100211.patch, hdfs-918-20100228.patch, 
> hdfs-918-20100309.patch, hdfs-918-branch20-append.patch, 
> hdfs-918-branch20.2.patch, hdfs-918-pool.patch, hdfs-918-TRUNK.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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