The CompositeCounter stores its 'children' in an IdentityHashMap. Consider using a different data structure, or if necessary, two data structures for this use case.

I am working on a high-performance application with many updates to the counters. From a recent Java Flight Recording, I noted that my application had generated 50GB on heap of Iterators from this class during a test run. Consider keeping an ArrayList of children (in addition to / instead of) a Map such that accessing the Collection of children becomes a heap-free operation.