LeaseManager operations are inefficient in 2.8.

After HDFS-6757, LeaseManager #removeLease became expensive.
HDFS-6757 changed the sortedLeases object from TreeSet to PriorityQueue.
Previously the remove(Object) operation from sortedLeases was O(log n) but after the change it became O( n) since it has to find the object first.
Recently we had an incident in one of our production cluster just hours after we upgraded from 2.7 to 2.8
The sortledLeases object had approximately 100,000 items within it.
While removing the lease, it will acquire the LeaseManager lock and that will slow down the lookup of lease also.

HDFS-6757 is a good improvement which replaced the path by inode id.