An issue was discovered in the noise_search crate through 2020-12-10 for Rust. There are unconditional implementations of Send and Sync for MvccRwLock.
https://rustsec.org/advisories/RUSTSEC-2020-0141.html
https://raw.githubusercontent.com/rustsec/advisory-db/main/crates/noise_search/RUSTSEC-2020-0141.md