Several followup items to potentially improve the performance of #11695.

• : Replace cluster metadata with slot specific dictionaries #11695 (comment)). Is this something we believe needs to be done now? [Madelyn votes no] MSET already has improved performance and this enhancement can be taken up in isolation.
• : Performance optimization for the index tree to find fair item in O(Log(N)) instead of O(Log^2(N)) (Followup seems okay here?) Optimize finding slot for a given key count in a fenwick tree #12704