HMGraphCache boxes a lot of integers

[dlg99]

private final Map<Integer, CachedNode> cache;

can be replaced with something like netty's io.netty.util.collection.IntObjectHashMap or similar to reduce this.

From JFR:

Class		Alloc Total	Total Allocation (%)
java.lang.Integer	1.2357043928E10 B	4.578557174712677 %		

There is no clear stack where the Integers are created, but this map is one of the suspect.

[jkni]

This seems worth addressing. Given the number of hops in our caching graph indexes and the boxing overhead, this could definitely be sizable allocation/heap footprint waste. When I tested specialized collections earlier to evaluate latency advantages, both fastutil and Eclipse Collections looked like strong candidates.

[jbellis]

I'm down for either fastutil (which has fastutil-concurrent-wrapper available as well) or agrona (which is what C* uses).