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https://issues.apache.org/jira/browse/HDFS-918?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jay Booth updated HDFS-918:
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Attachment: hdfs-918-20100228.patch
New patch -- Took Zlatin's advice and utilized selectionKey.interestOps(0) to
avoid busy waits, so we're back to a single selector and an ExecutorService.
The ExecutorService reuses threads if possible, destroying threads that haven't
been used in 60 seconds. Analyzed logs and the selectorThread doesn't seem to
busy wait ever. Buffers are now stored in threadlocals and allocated per
thread (they're now HeapByteBuffers since we might have some churn and most of
our transfer is using transferTo anyways). Still uses shared BlockChannelPool
implemented via ReadWriteLock.
I think this will be pretty good, will benchmark tonight.
> 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-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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