what are the disadvantages of RPC with respect to message passing?

Question

what are the disadvantages of RPC with respect to message passing?

Answer 1

Are you talking about RPC vs Messaging? As in (typically) asynchronous messaging? If that's what you're talking about, then Messaging tends to be more robust at the cost of complexity and extra infrastructure.

The simplest example is if you have a scenario where you RPC->RPC->RPC, you end up having a call stack that's 3 processes/machines deep. Any one of those processes/machine could fail during processing, and the entire stack unwinds.

If you were messaging, the actual connectivity between the processes is much less. You hand the message off, and you're on your way. Now if one of the processes fail, there's a good chance of it being restarted where it left off, since, typically, the message is still sitting on a queue somewhere waiting for a new process to fetch it. The overall time may be longer, but it's a much more robust system.

Mind it's no panacea, there are a lot of pitfalls with an asynchronous architecture, but this robustness is a prime distinction between RPC and Messaging systems.