TCP Fast Open: expediting web services

The normal technique is to mark all non-idempotent requests with a unique id, and keep track of which ones have already been processed. That is practically the only way to get once-only execution semantics.

This could presumably be done (up to a point) at the transport layer with TCP Fast Open by having the initiating endpoint assign a unique identifier to a given user space connection request, attaching the identifier as a TCP option, caching the identifier for some reasonable period on the target endpoint, and throwing away SYN packets with connection identifiers that have already been satisfied. The more general way to do that of course is to do it at the application layer, in addition to anything the transport layer may or may not do.