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MySQL Replication  /  Replication Configuration

Chapter 2 Replication Configuration

Replication between servers in MySQL is based on the binary logging mechanism. The MySQL instance operating as the replication source server (the source of the database changes) writes updates and changes as events to the binary log. The information in the binary log is stored in different logging formats according to the database changes being recorded. Replicas are configured to read the binary log from the source and to execute the events in the binary log on the replica's local database.

Important

You cannot configure the source to log only certain events.

The source is dumb in this scenario. Once binary logging has been enabled, all statements are recorded in the binary log. Each replica receives a copy of the entire contents of the binary log. It is the responsibility of the replica to decide which statements in the binary log should be executed; you cannot configure the source to log only certain events. If you do not specify otherwise, all events in the source's binary log are executed on the replica. If required, you can configure the replica to process only events that apply to particular databases or tables.

Each replica keeps a record of the binary log coordinates: The file name and position within the file that it has read and processed from the source. This means that multiple replicas can be connected to the source and executing different parts of the same binary log. Because the replicas control this process, individual replicas can be connected and disconnected from the server without affecting the source's operation. Also, because each replica records the current position within the binary log, it is possible for replicas to be disconnected, reconnect and then resume processing.

The source and each replica must be configured with a unique ID (using the server_id system variable). In addition, each replica must be configured with information about the source's host name, log file name, and position within that file. These details can be controlled from within a MySQL session using the CHANGE MASTER TO statement on the replica. The details are stored within the replica's connection metadata repository, which can be either a file or a table (see Section 5.2, “Relay Log and Replication Metadata Repositories”).

This section describes the setup and configuration required for a replication environment, including step-by-step instructions for creating a new replication environment. The major components of this section are: