Abseil provides its own family of hash tables (colloquially known as “Swiss tables”) in place of std::unordered_set and std::unordered_map. These classes are: absl::flat_hash_map absl::flat_hash_set absl::node_hash_map absl::node_hash_set This design note explains how these tables were implemented, the performance improvements our tables provide in certain cases, and why those might make you choose them over std::unordered_{set,map}. Lookup Optimizations Swiss tables hold a densely packed array ...