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https://issues.apache.org/jira/browse/HDFS-10817?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15468294#comment-15468294
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Erik Krogen commented on HDFS-10817:
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[~arpitagarwal], thank you for the concern but I do not believe that
understanding is correct. {{getReadHoldCount}} is checking how many reentrant
locking calls have been made. Each thread stores its own copy of
{{readLockHeldTimestamp}} (note that it is a {{ThreadLocal}}, meaning each
thread has its own copy) which is set on its first read lock call, and read on
its final unlock call. Different threads will each monitor and record their
time separately.
> Add Logging for Long-held NN Read Locks
> ---------------------------------------
>
> Key: HDFS-10817
> URL: https://issues.apache.org/jira/browse/HDFS-10817
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: logging, namenode
> Reporter: Erik Krogen
> Assignee: Erik Krogen
> Fix For: 2.8.0, 2.7.4, 3.0.0-alpha2
>
> Attachments: HDFS-10817.000.patch, HDFS-10817.001.patch,
> HDFS-10817.002.patch, HDFS-10817.003.patch, HDFS-10817.004.patch,
> HDFS-10817.addendum.000.patch, HDFS-10817.addendum.001.patch
>
>
> Right now the Namenode will log when a write lock is held for a long time to
> help tracks methods which are causing expensive delays. Let's do the same for
> read locks since these operations may also be expensive/long and cause
> delays.
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