https://blog.faceutil.com/2017/03/16/%eb%b3%b8%ea%b2%a9-%ec%9e%90%eb%a7%89-%ed%99%95%ec%9e%a5%ec%9e%90%eb%a5%bc-%eb%b3%80%ed%99%98%ec%8b%9c%ec%bc%9c%ec%a3%bc%eb%8a%94-%ed%94%84%eb%a1%9c%ea%b7%b8%eb%9e%a8-subresync-%e3%81%a0/