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https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12851869#action_12851869
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Jay Booth commented on HDFS-918:
--------------------------------
Weird. We've been running an almost-the-same version of the patch on our dev
cluster for a week and this version passed TestPRead and
TestDataTransferProtocol.. admittedly this isn't the exact version we ran on
our cluster so there could be a difference but it passes tests, I'm a little
stymied.
There weren't any exceptions or anything in the datanode log? That error will
typically happen when it tries and fails to read the block from where it should
be, so hopefully there will be some errors in the DN log.
> 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-918-branch20.2.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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