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https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12806461#action_12806461
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Todd Lipcon commented on HDFS-918:
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I think a main benefit of this work will be scalability with a high number of
concurrent connection.
A good test would be to write a quick MR job that opens a few hundred
DFSInputStreams from each mapper, all to the same block of the same file, and
reads very slowly on them (one byte every few seconds, for example). This
should be fine on actual disk IO since it will all hit the buffer cache, but
will demonstrate whether this has a scalability improvement over the
thread-per-reader.
> 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-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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