According to lmdb's doc, it seems that Env's mapsize can be resized after open as long as there's no active write transaction. http://www.lmdb.tech/doc/group__mdb.html#gaa2506ec8dab3d969b0e609cd82e619e5 "It may be called at later times if no transactions are active in this process."

However lmdbjava doesn't seem to have this capability. Please consider adding an API for this.