Mongos (and mongod) maintain connection pools wrapped by task executors. These pooled connections are used to perform RPC. Sometimes, these RPC operations come in 'bursts' and no pre-existing pooled connections are available to serve some operations. In these cases, operations are bottlenecked behind new-connection-establishment. We'd like to understand how much time is spent establishing new connections to better understand this potential bottleneck.

Let's create a measurement of wall-time for this new-connection establishment. 

Ideally, it would also be good to include partial measurements for each step of the connection establishment, including:

• Establishing the TCP connection/sockets.
• Resolving DNS
• Performing the TLS handshake
• MongoDB auth 

Including parts of the detailed breakdown, especially MongoDB auth, may be better suited to break-out into separate tickets after some investigation.