Keith Turner resolved ACCUMULO-4805.
    Resolution: Fixed

I did not remove the lock contention in the two PRs, I only made it less 
painful.  The global tserver lock is still there.  I did the following.
 *  made the code that executes when the lock is held faster
 * made a scan operation acquire the lock much fewer times
 * Changed semaphore from fair to non-fair, as the fair semaphore was very slow

I think it may be best to remove the file manager completely as described in 
ACCUMULO-543.  The only reservation is I have is continually deserializing the 
rfile metadata.

> Seeing thread contention on FileManager
> ---------------------------------------
>                 Key: ACCUMULO-4805
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-4805
>             Project: Accumulo
>          Issue Type: Bug
>            Reporter: Keith Turner
>            Assignee: Keith Turner
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.9.0, 2.0.0
>          Time Spent: 2h
>  Remaining Estimate: 0h
> Accumulo has a tablet server wide cache of open files.  Accessing this cache 
> obtains a global lock.  In profiling, I am seeing contention on this lock.

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