Understanding MySQL Replication: Does log_bin Log Everything Without Specifying Databases?

When setting up MySQL replication for multiple databases, confusion often arises regarding the binary log configuration. One common question is whether MySQL will log every change made to a database if you don’t specify any particular databases in the configuration file. In this post, we will demystify how MySQL’s binary logging works, especially when it comes to the binlog-do-db and binlog-ignore-db directives.

The Problem: How Does MySQL Handle Database Logging?

What Are Binary Logs?

Binary logs in MySQL are used to record changes made to the databases. These logs are essential for replication, helping slaves keep up-to-date copies of the master’s data. Understanding how to configure which databases are logged is crucial, especially when you’re working with multiple databases for different clients.

The Configuration Dilemma

While configuring your MySQL setup, you might wonder:

• Can I skip listing every database and just ignore a couple?
• If I specify to ignore certain databases, will everything else be logged appropriately?

To illustrate this scenario, let’s consider a typical my.cnf configuration file setup.

The Solution: Using binlog-ignore-db Effectively

Using binlog-ignore-db

You may choose to include specific ignore commands in your MySQL configuration. For instance:

binlog-ignore-db = mysql
binlog-ignore-db = informationschema

This configuration suggests that when a command is executed on the mysql or informationschema databases, those commands will not be logged. However, the crucial part lies in how the default database interacts with these commands.

Rules for Binary Logging

According to the MySQL documentation:

• If the default database matches any binlog-ignore-db rules, the statement will not be written to the log.
• If the default database does not match the ignored databases, the query will be logged.

This means that as long as you are executing commands on databases that do not match your ignore rules, those changes will be recorded in the binary logs.

Implications for Replication

When you remove the binlog-do-db entries, it may appear that everything is logged, as you will see changes in the binary log file. However, just logging everything doesn’t guarantee that these logs will be replicated on the slave server.

Possible Issues

• If no binlog-do-db specifications are made and the ignored databases do not match, MySQL might log everything, but the slave may not receive these changes.
• To resolve replication issues, you may need to use the replicate-do-db option on the slave, which could counter your streamlined configuration efforts.

Conclusion

The takeaway here is that omitting binlog-do-db entries while using binlog-ignore-db can lead to a scenario where MySQL logs everything except the ignored databases. However, it’s vital to ensure that you maintain the appropriate configurations on your slave server to ensure replication works effectively.

By understanding these configuration nuances, you can maintain a reliable MySQL replication setup without encountering unnecessary complexity in your configurations.

If you have any further questions about MySQL replication or configurations, feel free to reach out!