code: func (m *Meta) GenAutoTableID(dbID, tableID, step int64) (int64, error) {
  	// Check if DB exists.
  	dbKey := m.dbKey(dbID)
  	if err := m.checkDBExists(dbKey); err != nil {
  		return 0, errors.Trace(err)
  	}
  	// Check if table exists.
  	tableKey := m.tableKey(tableID)
  	if err := m.checkTableExists(dbKey, tableKey); err != nil {
  		return 0, errors.Trace(err)
  	}
  
  	return m.txn.HInc(dbKey, m.autoTableIDKey(tableID), step)
  }
docs: // GenAutoTableID adds step to the auto ID of the table and returns the sum.