Quite often we see that the main operational storage is used in conjunction with some additional services, for example, for caching or full-text search. Another architecture approach using multiple databases is microservices, where every microservice has its own database better optimized for the tasks of this particular service. For example, you can use MySQL for [&]

https://www.percona.com/blog/pros-and-cons-when-you-should-and-should-not-use-mongodb/