RPC stands for remote procedure calls.

Complexity and latency of RPC vs. local calls?

local call: pretty fast, only program counter or pointers change

RPC: involves marshalling/unmarshalling, error handling, authentication , authorization, session, heap manipulation.

Given that, in real life, RPC is useful. It can be used for those client who has small computing power and most of works will be finished at remote end.

What is IDL(Interface Description Language)?

It is a language that describe an interface in a language-independent way, which means that the communication between different software components can be written in different language(e.g c++, Java) . IDLs offer a bridge between the two different systems, therefore is commonly used in RPC. Example of it is JAVA, XML, Google protocol buffers.