I should emphasize that my question is in regard to CP (Consistent and Partition Tolerant) systems.
A lot of widely used NoSQL databases such as Mongo and Redis seem to fall in the CP category. And in addition to that, RDBMS's such as SQL Server and MySQL can also be configured to operate in a CP multi-master mode.
Two arguments I could find on the Internet are:
- Load balancing write queries
- Decreasing downtime in case of failure of a Master
I have doubts about the first reason because as far as I understand, in order to maintain data consistency between these Master replicas, the write operation should take place in every Master. If so, that will create the same burden for all the Masters plus the overhead associated for synchronization.
What are the solid reasons for such systems? Or am I missing something?