Practical limit to database size is around 1GB (even on 64-bit platforms). Multithreaded and multiuser access requires manual support from the programmer and is discouraged (in C++, TCL and Python use one automatically global lock). Combinations of more advanced features are often not tested and may fail. It is possible to obtain somewhat better performance than with other databases (published benchmarks include SQLite and Berkeley DB) but it requires lot of testing and lot of knowledge of Metakit internals. Metakit's API is low level, compared to SQL.