This is a test to check if my relayer will store this event locally and eventually rebroadcast.

Flatbuffers is a good choice. As long that it has a strict schema (to avoid storing metadata, like BSON/JSON).

Although my relayer is built in Rust, my top priority is to launch it as soon as possible. Once it's up and running, I can then focus on optimizing it further. The main requirement for the relayer is that the signature matches the reconstructed event, and that the content is compressed to minimize bandwidth usage.

In my own relayer, soon to be open source, I'm storing things as raw JSON. I am thinking to compress and store as binary (same format as the data to be signed). Maybe that will save some percentage.