In a previous post I showed how to implement multi-source round-robin replication in pure SQL using the tables that are needed for crash-safe replication. I also outlined a revised version of this approach in the Replication Tips & Tricks presentation I gave at MySQL Connect. This was, however, before the GTID (Global Transaction ID) implementation was done. Now that they are introduced, multi-source replication is even easier since you no longer have to keep track of the positions.

Figure 1. Tables for storing information about masters

CREATE TABLE my_masters (
    idx INT AUTO_INCREMENT,
    host CHAR(50) NOT NULL,
    port INT NOT NULL …

With the addition of the new tables to implement crash-safe replication we also get access to replication information through the SQL interface. This might not seem like a big advantage, but it should not be taken lightly. To demonstrate the power of using this approach, I will show how to implement a multi-source round-robin replication described at other places (including our book). However, compared to the other implementations—where the implementation requires a client to parse the output of SHOW SLAVE STATUS—the twist is that the implementation is entirely done in the server, using pure SQL.

If you're familiar with replication, you know that a slave can just …