ensures instrumented cache is recording stats

[keith-turner]

No description provided.

[keith-turner]

The motivation behind this is that in the past the scan servers tablet metadata cache was instrumented w/ micrometere but not recording stats. Was attempting to use the cache metrics and they were zero and/or non existent. Spent a long time tracking down why instrumentation was not working (was looking at micrometer source code first thinking there was a bug there). Finally realized it was a problem w/ how the cache was built, just happened to remember that recording stats is optional. So this change is an attempt to catch future changes where the cache is changed to no longer record stats. Tried to think of a more general way to catch this mismatch between cache builder and cahce insturmention that could catch the problem anywhere in the Accumulo code base, but could not think of anything. So this change adds a check to the place where I saw it and it caused me problems.

[cshannon]

This seems ok to me, is there any risk with having the state check being added in a minor release of causing anything to break on upgrade that we would not want to happen?

[keith-turner]

This seems ok to me, is there any risk with having the state check being added in a minor release of causing anything to break on upgrade that we would not want to happen?

I think the risk of this change is low because its one part of code checking another part of the code that is not configurable. So the user can not do anything ATM that would trigger this new check. It should only be triggered by a code change that disables recording stats when the cache is constructed.