MySQL Troubleshooting

Chapter 5. Troubleshooting Replication

I already touched on replication issues in previous chapters, showing how the problems discussed in each chapter can affect replicated environments. This chapter focuses on issues specific to replication itself. These are mostly replication failures due to errors or slowdowns, such as a slave that lags several hours behind the master.

MySQL’s replication is asynchronous. This means the master does not care whether data on the slave is consistent. Although circular multiple master replication can be set up, in a practical sense it is a chain of servers, with each of them serving as a slave and a master at the same time.

MySQL Multiple Master Setup

To illustrate the concept behind MySQL multiple master replication, let’s consider Figure 5-1.

Figure 5-1. Two servers that replicate each other

Here server A is a master of its slave B, and at the very same time, server B is a master of slave A.

You can add as many servers as you wish to such chains (Figure 5-2).

Figure 5-2. Circular replication with multiple servers

To troubleshoot such setups, you need to take a single master/slave pair (Figure 5-3).

Figure 5-3. Focusing on one direction in multimaster ...