In Volo 0.9.0, we mainly changed the default generated HashSet/HashMap type to AHashMap/AHashSet, which is expected to bring certain performance improvements. Additionally, with the release of Rust 1.75 , Volo is already available in stable rust. Break Change Modification of the default generated HashSet / HashMap type In the new version of the generated code, the default generated HashMap/HashSet type is changed to AHashMap/AHashSet, which gives better performance than std map, refer to ahash .