MySQL replication in action - Part 5 - parallel appliers

Previous episodes:

• MySQL replication monitoring 101
• MySQL replication in action - Part 1: GTID & Co
• MySQL replication in action - Part 2 - Fan-in topology
• MySQL replication in action - Part 3 - All-masters P2P topology
• MySQL replication in action - Part 4 - star and hybrid topologies

Parallel replication overview

One of the main grievance of replication users is that, while a well tuned master server can handle thousands of concurrent operations, an equally tuned slave is constrained to work on a single thread. In Figure 1, we see the schematics of this paradigm. Multiple operations on the master are executed simultaneously and saved to the binary log. The slave IO thread copies the binary log events to a local log, and on such log the SQL thread executes the events on the slave database. When the master is very active, chances are that the slave lags behind, causing hatred and nightmares to the DBAs.

Figure 1 - Single applier