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MySQL 8.4 Reference Manual  /  Replication

Chapter 19 Replication

Table of Contents

19.1 Configuring Replication
19.1.1 Binary Log File Position Based Replication Configuration Overview
19.1.2 Setting Up Binary Log File Position Based Replication
19.1.3 Replication with Global Transaction Identifiers
19.1.4 Changing GTID Mode on Online Servers
19.1.5 MySQL Multi-Source Replication
19.1.6 Replication and Binary Logging Options and Variables
19.1.7 Common Replication Administration Tasks
19.2 Replication Implementation
19.2.1 Replication Formats
19.2.2 Replication Channels
19.2.3 Replication Threads
19.2.4 Relay Log and Replication Metadata Repositories
19.2.5 How Servers Evaluate Replication Filtering Rules
19.3 Replication Security
19.3.1 Setting Up Replication to Use Encrypted Connections
19.3.2 Encrypting Binary Log Files and Relay Log Files
19.3.3 Replication Privilege Checks
19.4 Replication Solutions
19.4.1 Using Replication for Backups
19.4.2 Handling an Unexpected Halt of a Replica
19.4.3 Monitoring Row-based Replication
19.4.4 Using Replication with Different Source and Replica Storage Engines
19.4.5 Using Replication for Scale-Out
19.4.6 Replicating Different Databases to Different Replicas
19.4.7 Improving Replication Performance
19.4.8 Switching Sources During Failover
19.4.9 Switching Sources and Replicas with Asynchronous Connection Failover
19.4.10 Semisynchronous Replication
19.4.11 Delayed Replication
19.5 Replication Notes and Tips
19.5.1 Replication Features and Issues
19.5.2 Replication Compatibility Between MySQL Versions
19.5.3 Upgrading or Downgrading a Replication Topology
19.5.4 Troubleshooting Replication
19.5.5 How to Report Replication Bugs or Problems

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 Section 19.4, “Replication Solutions”.

MySQL 8.4 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 19.1.3, “Replication with Global Transaction Identifiers”. For information on using binary log file position based replication, see Section 19.1, “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 Chapter 25, MySQL NDB Cluster 8.4). In MySQL 8.4, 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 19.4.10, “Semisynchronous Replication”. MySQL 8.4 also supports delayed replication such that a replica deliberately lags behind the source by at least a specified amount of time; see Section 19.4.11, “Delayed Replication”. For scenarios where synchronous replication is required, use NDB Cluster (see Chapter 25, MySQL NDB Cluster 8.4).

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 19.1.2, “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 19.2.1, “Replication Formats”.

Replication is controlled through a number of different options and variables. For more information, see Section 19.1.6, “Replication and Binary Logging Options and Variables”. Additional security measures can be applied to a replication topology, as described in Section 19.3, “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 Section 19.4, “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 Section 19.5, “Replication Notes and Tips”. For answers to some questions often asked by those who are new to MySQL Replication, see Section A.14, “MySQL 8.4 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 Section 19.2, “Replication Implementation”.