As described in the diagnosis/debuggability section of the design document, the following behavior should be added:

1. Log to the config server primary’s main log timing stats at each phase of the transaction used to refine a collection’s shard key.
   • e.g. before and after updating the collection document, after updating each chunk, and after updating each zone range.
2. Add change log writes at beginning and end of refining a shard key.