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https://issues.apache.org/jira/browse/HDFS-6093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13935723#comment-13935723
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Colin Patrick McCabe commented on HDFS-6093:
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This looks good overall. I think rather than protect
{{CacheReplicationMonitor#numPendingCaching}} with the FSN lock, it would be
better to make it an Atomic64 that we swap in at the end of the rescan. That
way we're not baking in the assumption that the rescan thread holds the FSN
lock for the whole duration of the rescan. It also would minimize the time we
spend blocking waiting for the FSN lock in the MBean stuff.
> Expose more caching information for debugging by users
> ------------------------------------------------------
>
> Key: HDFS-6093
> URL: https://issues.apache.org/jira/browse/HDFS-6093
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: caching
> Affects Versions: 2.4.0
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Attachments: hdfs-6093-1.patch
>
>
> When users submit a new cache directive, it's unclear if the NN has
> recognized it and is actively trying to cache it, or if it's hung for some
> other reason. It'd be nice to expose a "pending caching/uncaching" count the
> same way we expose pending replication work.
> It'd also be nice to display the aggregate cache capacity and usage in
> dfsadmin -report, since we already have have it as a metric and expose it
> per-DN in report output.
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