Data structure to hold RegionInfo and the address for the hosting
HRegionServer. Immutable. Comparable, but we compare the 'location' only:
i.e. the hostname and port, and *not* the regioninfo. This means two
instances are the same if they refer to the same 'location' (the same
hostname and port), though they may be carrying different regions.
On a big cluster, each client will have thousands of instances of this object, often
100 000 of them if not million. It's important to keep the object size as small
This interface has been marked InterfaceAudience.Public in 0.96 and 0.98.