MySQL replication does not always scale up well. A common reason for
that is the single-threaded nature of the slave server applier.
Indeed the performance race between the master and the slave
has been unfair. Contrary to the master, which executes transactions
concurrently by multiple threads, the standard MySQL slave is limited
to install changes sequentially by the only thread.
However, if logical partitioning of data per database
takes place, the 5.6 server's Multi-Threaded Slave (MTS) framework may
be found helpful. It allows to install changes done to different
databases in parallel.
For instance the simplest use case would be when the master server has
just two databases and transactions against the master server update
only one of them at a time. Those transactions when replicated will
be executed by two separate slave worker …