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https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844280#action_12844280
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Todd Lipcon commented on HDFS-918:
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bq. I think it is better to use something like Netty rather than worry about
all the selector handling as in this patch.
I started some work on this last month and got a prototype working. The issue
is that switching to Netty is rather wholesale - all of the existing code has
to change away from using InputStream/OutputStream to use the Netty Channels. I
managed to write some interfacing code to provide IS/OS interfaces around the
Netty channels and got unit tests to pass, but there's a lot of inefficiency
introduced by my wrappers.
I'll continue to work on that as I have time, but I think this smaller patch is
worth considering in the meantime.
> 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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