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https://issues.apache.org/jira/browse/HDFS-10872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15589506#comment-15589506
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Zhe Zhang commented on HDFS-10872:
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Thanks for the discussion Andrew and Erik.
I agree that moving the multi-threading logic to Metrics classes is a good
idea. I'm actually pretty curious how that will improve the performance of
existing RPC metrics collection; it seems pretty expensive. We should probably
do that as a prerequisite and then rebase this patch.
Using {{LongAdder}} is an interesting idea. [~andrew.wang] This is actually the
first time I learn about it :) Are we aware of any production usage of this
library? I took a look at the test coverage; it seems a little weak considering
the complexity of the main logic. We can probably consider adding some more
unit tests in Hadoop to cover cases we are most interested in.
I expect that a few minutes after the NN starts, the set of operations (keys)
in the {{opHoldtimeMetrics}} map is stablized. Afterwards, each entry is
essentially a counter to be incremented. So on the high level I think we should
be able to make it work with {{LongAdder}}. Agreed with [~xkrogen] that
snapshotting/resetting is probably the trickiest part. Creating a new
{{LongAdder}} in {{snapshot}} sounds reseaonable to me.
> 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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