MySQL 5.6 Replication - Enabling the Next Generation of Web & Cloud Services

From: http://dev.mysql.com/tech-resources/articles/mysql-5.6-replication.html

Multi-Threaded Slaves

Replication performance is improved by using multiple execution threads to apply replication events to the slave(s).

The multi-threaded slave splits processing between worker threads based on schema, allowing updates to be applied in parallel, rather than sequentially. This delivers benefits to those workloads that isolate application data using databases - e.g. multi-tenant systems

To demonstrate performance benefits of Multi-Threaded Slaves, the MySQL Engineering team recently completed a benchmark that compared slave throughput when using single and multi-threaded replication. As the results below demonstrate, slave throughput was increased by ~ 5x based on a configuration with 10 databases/schemas, directly translating to improved read consistency and reduced risk of data loss in the event of an outage of the master.

Slaves are better able to keep up with the master, and so users are much less likely to need to throttle the sustained throughput of writes, just so that the slaves don't indefinitely fall further and further behind (at the moment some users have to reduce the capacity of their systems in order to reduce slave lag).