code: func writeSystemTZ(s Session) {
  	sql := fmt.Sprintf(`INSERT HIGH_PRIORITY INTO %s.%s VALUES ("%s", "%s", "TiDB Global System Timezone.") ON DUPLICATE KEY UPDATE VARIABLE_VALUE="%s"`,
  		mysql.SystemDB, mysql.TiDBTable, tidbSystemTZ, timeutil.InferSystemTZ(), timeutil.InferSystemTZ())
  	mustExecute(s, sql)
  }
docs: // writeSystemTZ writes system timezone info into mysql.tidb