建议何时/如何将数据保存到数据库，何时插入到MongoDB

I am developing an application architecture that allows users to add some data like reviews on some product, along with signup/signin features. For quick insert and get i am thinking about using MongoDB, and for persistence storage (in case mongodb gets corrupt or fail) i would like to save that to a database (postgre/msql). Also for signup/signin i would be doing the same.I am developing an application architecture tha