Metrics for tracking offending queries

I have seen big GC pauses leading to nodes being marked DOWN in our cluster. The most common issue is someone, would add a large range scan and it would be difficult to pin-point the specific query. I have added a mechanism to account the memory allocation for a specific query. In order to allow aggregates over a period I added a metric as well. Attached is the diff.

I was wondering if something like this would be interesting for more general audience. There are some things which need to be fixed for proper release. For instance, Cleaning up existing metrics on server restart. However, just wanted to check before that if something like this would be useful for others.