public class CollectionMetricHelper
Encapsulates various interesting statistics involving collections.
The rationale behind this class:
we have various classes that can look up information about collections from various sources -- ZookeeperAPI, CollectionAPI, MBeanAPI.
So if you are looking for something about a collection you need to know some implementation details about where that
information is available.
This is an attempt to abstract away those implementation details, so that you have one place to go to get information
about a collection.
The client-facing frontend for this is CollectionResource.
If we want to poll Solr's JMX endpoints or other stat sources to track # of requests over time and similar
time-series stats, this is a potential place to do it.