In many cases when diagnosing the behavior of a sharded cluster, there has been a need to better understand the current behavior of what the mongos is doing. We have often been able to work around this, but it would be much more direct and clear if we could just directly query the current state of routing operations. To this end, I suggest the creation of a currentRouterOps command (name not important). When called against a mongos, it would generate that would include:

For each inbound request from clients:

• client host:port
• what the operation is
• time of arrival
• if there's any classification the mongos does of ops (scatter/gather, directly steered, etc), include that
• which backend(s) (shard mongod or config server) it determined to route the op to
  • for each backend, what role it plays (i.e. in a scatter/gather, who are the scatterers vs gatherer)
  • which connection(s) are being used for that backend
  • current believed status of that op on the backend.

While this would be good for future versions, please consider adding it to all non-EOL versions of mongos.