Comment by boulos

You should probably use either boost::unordered_flat_map or absl::flat_hash_map if you don't need ordering. Especially with 20-byte values. (Though you didn't mention the key type). If you're dealing with building against Boost already, I'd just switch and measure it.

https://github.com/boostorg/boost_unordered_benchmarks/tree/... (Via a response from the boost authors in https://www.reddit.com/r/cpp/comments/yikfi4/boost_181_will_...) has more benchmarks depending on your pattern.