Because JSON is around twice as fast to encode/decode in Node, which is where I really need the performance. MessagePack is just slow, complicated, and unnecessary.
Good point... a Node MQ project formerly based on msgpack recently switched to JSON and increased its performance by almost 200%: https://github.com/aikar/wormhole/issues/3
I've done several of my own benchmarks as well and can confirm that the current Node JSON implementation is much faster than MessagePack. Their benchmarks are most likely quite old.
That mostly speaks to the quality of node's MessagePack implementation, nothing more. Benchmarking data format serialization is hard, because one poor implementation throws things off.
There are benefits to MessagePack that have already been mentioned here, namely not having to base64 binary data first (smaller size), but that's true for any binary message format. I'd love to see some other binary formats thrown into the ring and see how they compare to MessagePack in both size efficiency and encode/decode performance. BSON seems like an interesting option, but I don't know enough about it to comment...
True, but, optimization is tricky, and you can say the say thing about ruby's messagepack and JSON libraries, where the speed difference is reversed. I, unfortunately don't have the time to go digging as to why, but there's a discrepancy somewhere.
