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https://issues.apache.org/jira/browse/HDFS-9952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15197381#comment-15197381
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Daryn Sharp commented on HDFS-9952:
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Nice. I've been meaning to add these metrics for quite awhile now. A few
issues:
# I'm not sure if metrics can be null, but I see some places doing the same
check. So if it can go null, {{NameNode.getNameNodeMetrics()}} must be called
once to assign, null checked, used.
# Write lock wait should only be updated in the "if" for first write lock.
Otherwise reentrant locking (with near 0 time) will dilute the value.
# Most importantly and adamantly, {{MutableRate#add}} is synchronized in an
extremely critical code path which will destroy concurrent read ops.
Synchronization will not scale with 100 threads doing 20-40k ops/sec, with
bursts of 60-100k+ ops/ sec. I'm not a metrics expert but this must use a
non-synchronized metric.
> Expose FSNamesystem lock wait time as metrics
> ---------------------------------------------
>
> Key: HDFS-9952
> URL: https://issues.apache.org/jira/browse/HDFS-9952
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Vinayakumar B
> Assignee: Vinayakumar B
> Attachments: HDFS-9952-01.patch
>
>
> Expose FSNameSystem's readlock() and writeLock() wait time as metrics.
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