02 / TRANSPORT

A connection is not a page.

It is easy to draw a request as a single arrow. In practice, the arrow may involve several conversations. A browser connects to a frontend, and that frontend may create another connection to an application.

Follow both sides.

A persistent connection from the browser does not prove that the frontend reuses its upstream connection. Check both boundaries. A frontend can keep the client socket alive while paying for a new upstream handshake on every request.

Reuse changes the cost.

Reusing an established connection can avoid parts of connection setup. It does not eliminate application processing, congestion or the time required to transfer bytes. The first request and the tenth request should therefore be measured separately.

Do not confuse settings with evidence.

A configuration directive describes an intention. Counters, connection traces and matched measurements show whether the intention is being realised. Verify that reuse actually happens before attributing an improvement to it.

Good diagrams show where connections begin and end. Good measurements use the same boundaries.