What are the advantages and disadvantages of splitting one database into several?

Question

MySQL

There are modules Geo, Places, Reviews, Users, Images. What problems might I run into if I decide to store each module's data in a separate database?

Answer 1

I will summarize here
1) JOIN between tables will be difficult to put it mildly
2) Little things like raising N connections instead of one
3) Keep N settings in the configs accordingly
4) connection - this operation is not free, as well as disconnection
5) There is a suspicion that not everything is with migrations either it will be smooth and silky
6) Consistency without transactions is a separate popabol.
The benefits are exactly zero, in any case, I could not come up with a single argument about it.

Answer 2

There can be only one advantage from this approach - isolation in a microservice architecture. If you don’t build it, then you definitely need to beat your hands for this because of the additional load and opacity. Also, there will be trouble with transactions, probably.