You are right, the client is using blocking I/O. Not to make excuses, but 2 years ago, when the client was developed, Rust’s support for async I/O wasn’t very mature yet, so the client only supports sync I/O. And despite initial interest in a Rust client we have not actually seen much usage of the client since then. We also believe that Rust has the potential to perform as good or even better than the Go client, but a lot more time and effort have been poured into optimizing the Go client (as well as the C, C# and Java clients).
Are you trying to make a decision whether to use the Rust or Go client? Or do you want to use the Rust client but need better performance than the client can currently support? What are your specific requirements?