Zheng Shao created HDFS-11586:
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Summary: Report %free, %write_locked, %read_locked for the
NameNode FSNamesystemLock
Key: HDFS-11586
URL: https://issues.apache.org/jira/browse/HDFS-11586
Project: Hadoop HDFS
Issue Type: Improvement
Components: namenode
Reporter: Zheng Shao
Priority: Minor
It's useful to understand how busy the NameNode is by providing these metrics,
similar to the %util number from iostat for disks.
When %free goes to close to 0, we know the NameNode is congested (just like
when disk %util goes to 100%).
This can be implemented very cheaply by using a thread that wakes up every 10ms
to check FSNamesystemLock's getReadLockCount() and isWriteLocked() (via the
member coarseLock).
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