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https://issues.apache.org/jira/browse/HDFS-7836?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14345475#comment-14345475
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Colin Patrick McCabe commented on HDFS-7836:
--------------------------------------------
Thanks, Yi. We'll definitely provide a webex.
I think moving the BRs out from under the FSN lock is more work than it seems,
and difficult to do incrementally. There are a lot of cases where we access
blocks in FSNamesystem, assuming that the FSN lock is sufficient protection
(or, to be pedantically correct, the FSDirectory lock in really recent
versions). Sure, we could have a separate BlockManager lock and take that, but
then we'd have to wait for that lock, while holding the FSN lock, which would
be disastrous for performance. The locking change is going to have to be done
as part of the sharding and other refactors in order to be beneficial.
> BlockManager Scalability Improvements
> -------------------------------------
>
> Key: HDFS-7836
> URL: https://issues.apache.org/jira/browse/HDFS-7836
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Charles Lamb
> Assignee: Charles Lamb
> Attachments: BlockManagerScalabilityImprovementsDesign.pdf
>
>
> Improvements to BlockManager scalability.
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