elsa VS SBE

First of all, you're comparing this to GSON and Kryo, how does it compare to Msgpack, fast-serialization, but also Elsa and I'm sure, many others? Are there any limitations and/or trade-offs?

I was about to suggest Chronicle, but it looks like they have gone closed-source. The older version is still interesting to look through though. Aeron / Disruptor / SBE are good projects for inspiration as well.

Could you evaluate how it compares with SBE?

The Simple Binary Encoding (SBE) project now includes support for generating Rust code. Generated code produced does not use unsafe and has no dependencies on any other crates.

SBE

Consider a valid protobuf message with such a field. If you can locate the field value bytes, you can write a new value to the same location without breaking the message. It's obviously possible to the same with the varint type too, as long as you don't change the number of bytes - not so practical, but useful for enum field which has a limited set of useful values (usually less than 128).

Pregenerating protobuf messages you want to send and then modifying the bytes in-place before sending is going to give you a nice performance boost over "normal" protobuf serialization. It can be useful if you need to be protobuf compatible, but it's obviously better to use something like SBE - https://github.com/real-logic/simple-binary-encoding