Historically MySQL is great in horizontal READ scale. The scaling, in that case, is offered by the different number of Replica nodes, no matter if using standard asynchronous replication or synchronous replication.
However, those solutions do not offer the same level of scaling for writes operation.
Why? Because the solutions still rely on writing in one single node that works as Primary. Also, in the case of multi-Primary, the writes will be distributed by transaction. In both cases, when using virtually-synchronous replication, the process will require certification from each node and local (by node) write; as such, the number of writes is NOT distributed across multiple nodes but duplicated.
The main reason behind this is that MySQL is a relational database system (RDBMS), and any data that is going to be written in it must respect the RDBMS …[Read more]