[kasey_junk]

I'd add that SBE is targeting the FIX community, where there are many, but bounded message types and the incidence of lists (or lists of lists) is rare and already segmented to the sections of systems that people associate with lower performance requirements.

Cap'n Proto does not seem to have this focus (forgive me for assumptions about intentions) and therefore is more designed around supporting the general data structure case.

I'd say that in the cases where the performance differences between these 2 systems really matter you would be unable to make a fair judgement without implementing your real world problem in both and testing the differences. That said, I had an argument today with a colleague about stop bit encoding vs fixed width encoding and without testing real world solutions I was hesitant to make any claims, even though my experience and bias would be toward fixed width encoding.

As for Protobuf, it has been a while since I've worked with them, but when I did I had 2 specific performance bottle necks other than the variability (on the JVM) 1) was encoding non-primitive fields and 2) was not being able to do allocation free programming with them.