The query subsystem uses Collection::numRecords() to retrieve estimated collection document count for the count command, $collStats stage and a proposed $approxCount stage. If used within a transaction this API does not provide a point in time estimate and the values returned will continue to change as collection writes occur. This request is to provide a snapshot mechanism for this information that will be safe to use within transaction allowing us to consider allowing use of $approxCount (and maybe $collStats with count) in a transaction.