code: public Stat stat() {
      if (closed) {
        throw new AlreadyClosedException();
      }
      final MDB_stat stat = new MDB_stat(RUNTIME);
      checkRc(LIB.mdb_env_stat(ptr, stat));
      return new Stat(
          stat.f0_ms_psize.intValue(),
          stat.f1_ms_depth.intValue(),
          stat.f2_ms_branch_pages.longValue(),
          stat.f3_ms_leaf_pages.longValue(),
          stat.f4_ms_overflow_pages.longValue(),
          stat.f5_ms_entries.longValue());
    }
docs: Return statistics about this environment.
  
  @return an immutable statistics object.