I understand that MongoDB supports the concept of capped collections where the max size of the collection can be specificied and that the size of an instance/cluster can be configured. If there are multiple DBs on a single instance/cluster, it would be nice if thesize of a single DB could be capped or otherwise limited.  The use case is that if you have a DBs per tenant that is on a shared instance, it would be nice to limit the extent to which a big neighbor can affect the instance/clusters health.