MySQL Replication  /  Replication

Chapter 1 Replication

Replication enables data from one MySQL database server (known as a source) to be copied to one or more MySQL database servers (known as replicas). Replication is asynchronous by default; replicas do not need to be connected permanently to receive updates from a source. Depending on the configuration, you can replicate all databases, selected databases, or even selected tables within a database.

Advantages of replication in MySQL include:

  • Scale-out solutions - spreading the load among multiple replicas to improve performance. In this environment, all writes and updates must take place on the source server. Reads, however, may take place on one or more replicas. This model can improve the performance of writes (since the source is dedicated to updates), while dramatically increasing read speed across an increasing number of replicas.

  • Data security - because the replica can pause the replication process, it is possible to run backup services on the replica without corrupting the corresponding source data.

  • Analytics - live data can be created on the source, while the analysis of the information can take place on the replica without affecting the performance of the source.

  • Long-distance data distribution - you can use replication to create a local copy of data for a remote site to use, without permanent access to the source.

For information on how to use replication in such scenarios, see Chapter 3, Replication Solutions.

MySQL 8.0 supports different methods of replication. The traditional method is based on replicating events from the source's binary log, and requires the log files and positions in them to be synchronized between source and replica. The newer method based on global transaction identifiers (GTIDs) is transactional and therefore does not require working with log files or positions within these files, which greatly simplifies many common replication tasks. Replication using GTIDs guarantees consistency between source and replica as long as all transactions committed on the source have also been applied on the replica. For more information about GTIDs and GTID-based replication in MySQL, see Section 2.3, “Replication with Global Transaction Identifiers”. For information on using binary log file position based replication, see Chapter 2, Configuring Replication.

Replication in MySQL supports different types of synchronization. The original type of synchronization is one-way, asynchronous replication, in which one server acts as the source, while one or more other servers act as replicas. This is in contrast to the synchronous replication which is a characteristic of NDB Cluster (see MySQL NDB Cluster 8.0). In MySQL 8.0, semisynchronous replication is supported in addition to the built-in asynchronous replication. With semisynchronous replication, a commit performed on the source blocks before returning to the session that performed the transaction until at least one replica acknowledges that it has received and logged the events for the transaction; see Section 3.10, “Semisynchronous Replication”. MySQL 8.0 also supports delayed replication such that a replica deliberately lags behind the source by at least a specified amount of time; see Section 3.11, “Delayed Replication”. For scenarios where synchronous replication is required, use NDB Cluster (see MySQL NDB Cluster 8.0).

There are a number of solutions available for setting up replication between servers, and the best method to use depends on the presence of data and the engine types you are using. For more information on the available options, see Section 2.2, “Setting Up Binary Log File Position Based Replication”.

There are two core types of replication format, Statement Based Replication (SBR), which replicates entire SQL statements, and Row Based Replication (RBR), which replicates only the changed rows. You can also use a third variety, Mixed Based Replication (MBR). For more information on the different replication formats, see Section 5.1, “Replication Formats”.

Replication is controlled through a number of different options and variables. For more information, see Section 2.6, “Replication and Binary Logging Options and Variables”. Additional security measures can be applied to a replication topology, as described in Replication Security.

You can use replication to solve a number of different problems, including performance, supporting the backup of different databases, and as part of a larger solution to alleviate system failures. For information on how to address these issues, see Chapter 3, Replication Solutions.

For notes and tips on how different data types and statements are treated during replication, including details of replication features, version compatibility, upgrades, and potential problems and their resolution, see Chapter 4, Replication Notes and Tips. For answers to some questions often asked by those who are new to MySQL Replication, see MySQL 8.0 FAQ: Replication.

For detailed information on the implementation of replication, how replication works, the process and contents of the binary log, background threads and the rules used to decide how statements are recorded and replicated, see Chapter 5, Replication Implementation.