code: public Stat stat(final Txn<T> txn) {
      if (SHOULD_CHECK) {
        requireNonNull(txn);
        txn.checkReady();
      }
      final MDB_stat stat = new MDB_stat(RUNTIME);
      checkRc(LIB.mdb_stat(txn.pointer(), 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 database.
  
  @param txn transaction handle (not null; not committed)
  @return an immutable statistics object.