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https://issues.apache.org/jira/browse/HDFS-10872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15587087#comment-15587087
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Andrew Wang commented on HDFS-10872:
------------------------------------
Thanks for working on this folks, and sorry for coming to this review late. I
have a few comments looking at this patch:
* I'd prefer we use try/finally to do the lock/unlocks in aggregateMetrics for
safety.
* We're doing the thread-local increment and aggregate outside of the metrics
system right now. Did we look into making the metrics classes themselves
multi-threading friendly? Then we could more easily reuse this code in other
places.
* Related, the aggregation right now is done periodically on increment. I think
what we'd really like is aggregate-on-read. The metrics classes support this
via {{setChanged}} and {{snapshot}}. Otherwise, occasionally one operation is
getting hit with the penalty of aggregating all the metrics, and possibly for
no reason if it's not being read.
I might have mentioned this before, but the
[LongAdder|http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/LongAdder.java?view=co]
code in JDK8 is basically what I'm thinking of, and the performance is quite
good. The license is friendly, so we could copy-paste this into Hadoop for the
branch-2's, and use the built-in JDK8 version for trunk.
> Add MutableRate metrics for FSNamesystemLock operations
> -------------------------------------------------------
>
> Key: HDFS-10872
> URL: https://issues.apache.org/jira/browse/HDFS-10872
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Erik Krogen
> Assignee: Erik Krogen
> Attachments: FSLockPerf.java, HDFS-10872.000.patch,
> HDFS-10872.001.patch, HDFS-10872.002.patch, HDFS-10872.003.patch,
> HDFS-10872.004.patch
>
>
> Add metrics for FSNamesystemLock operations to see, overall, how long each
> operation is holding the lock for. Use MutableRate metrics for now.
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