Scaling Instant Messaging communication services: A comparison of blocking and non-blocking techniques

Designing innovative communications services that scale to facilitate potential new usage patterns can pose significant challenges. This is particularly the case if these services are to be delivered over existing protocols and interoperate with legacy services. This work explores design choices for such a service: large scale message delivery to existing Instant Messaging users. In particular we explore message throughput, accuracy and server load for several alternative implementation strategies. These strategies focus on approaches to concurrency, with best practice in current and emerging techniques thoroughly benchmarked. Specifically, a conventional Java Executor approach is compared with a functional approach realised through Scala and its Actors framework. These could be termed “blocking I/O” technology. A third approach has also been measured - a “non-blocking I/O” based on an alternative to Java Virtual Machine approaches - employing Node.js and Javascript. We believe that some of the results are startling.