Several Boost authors have embarked on a project to improve the performance of boost's associative containers.

Boost.Unordered

by boost.org

About the improvements:

Boost.Unordered's new implementation of std::unordered_map (and multimap, set and multiset variants), and to extend its portfolio of available containers to offer faster, non-standard alternatives based on open addressing.

The first goal of the project has been completed in time for Boost 1.80 (due August 2022). We describe here the technical innovations introduced in boost::unordered_map that makes it the fastest implementation of std::unordered_map on the market.