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 …
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