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https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12801718#action_12801718
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Todd Lipcon commented on HDFS-839:
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Dhruba: regarding NN performance, do you often find that CPU or network are
limiting factors on your NNs? In my experience, the bottlenecks on the NN are
(a) RAM, and (b) the coarse grained FSNamesystem synchronization. That is to
say, CPU is only a bottleneck in that it can't begin to saturate all the cores
of a multicore system.
Given that, I imagine that the overhead of the NN having to forward block
reports, etc, over to even several BNs should be fairly low. It also short
circuits a bunch of tricky consistency questions if the DNs are reporting to
multiple places. (I'm assuming that all the BN synchronization work can be
deferred to other threads and shouldn't put any additional load on the
FSNamesystem lock)
> The NameNode should forward block reports to BackupNode
> -------------------------------------------------------
>
> Key: HDFS-839
> URL: https://issues.apache.org/jira/browse/HDFS-839
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: name-node
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
>
> The BackupNode (via HADOOP-4539) receives a stream of transactions from
> NameNode. However, the BackupNode does not have block locations of blocks. It
> would be nice if the NameNode can forward all block reports (that it receives
> from DataNodes) to the BackupNode.
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