code: func PgRelationSize(db XODB, v0 pgtypes.Regclass, v1 pgtypes.Regclass, v2 string) (int64, error) {
  	var err error
  
  	// sql query
  	const sqlstr = `SELECT pg_catalog.pg_relation_size($1, $2, $3)`
  
  	// run query
  	var ret int64
  	XOLog(sqlstr, v0, v1, v2)
  	err = db.QueryRow(sqlstr, v0, v1, v2).Scan(&ret)
  	if err != nil {
  		return 0, err
  	}
  
  	return ret, nil
  }
docs: // PgRelationSize calls the stored procedure 'pg_catalog.pg_relation_size(regclass, regclass, text) bigint' on db.