MySQL or PostgreSQL replication in case of network problems. Underwater rocks?

Question

MySQL

The problem is this. What to do and how to deal with the next problem.
We have several application servers that go to one database. We create a master-slave - let's call them db1 and db2 and everything seems to be ok. So, we get a problem with the network between one application server and the database, we start to assume that this db1 (master) server has fallen and make the master out of the db2 slave. At the same time, the second application server has no problems with the grid and quietly writes to db1. And it turns out that we have two masters at the same time.
How to deal with such a problem on PostgreSQL and MySQL?

Answer 1

https://en.wikipedia.org/wiki/STONITH
but in general, you have to choose between A and C in the end
https://ru.wikipedia.org/wiki/%D0%A2%D0%B5%D0%BE% D...