Details
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Improvement
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Status: Open
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Minor
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Resolution: Unresolved
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None
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None
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Description
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).