Does PostgreSQL *guarantee* that once the connection used to send the cancellation request is closed by the server, the cancellation has been delivered (as mentioned by Tom)? In other words, should I be designing a .NET driver around this behavior?
I'm not sure if there's some sort of feature/request list for protocol 4, but it may make sense to provide a simpler solution for this problem. One example would be for the client to send some sort of numeric ID identifying each comment (some autoincrement), and to include that ID when cancelling. I'm not sure the benefits are worth the extra payload but it may be useful for other functionality as well (tracking/logging)? Just a thought.
