The presentation will cover a new OCaml persistent-on-disk key-value store library. The library uses a B-tree library introduced at OCaml’17. The B-tree code has been extensively reworked to make it fast, and to support both copy-on-write and mutate-in-place operations. On top of this core, we include a write-ahead log, session initialization and termination, and extensive LRU-style caching. The API supports various “sync” operations, analogous to those found in filesystems.