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MySQL 8.2 Reference Manual  /  Replication

Chapter 17 Replication

Table of Contents

17.1 Configuring Replication
17.1.1 Binary Log File Position Based Replication Configuration Overview
17.1.2 Setting Up Binary Log File Position Based Replication
17.1.3 Replication with Global Transaction Identifiers
17.1.4 Changing GTID Mode on Online Servers
17.1.5 MySQL Multi-Source Replication
17.1.6 Replication and Binary Logging Options and Variables
17.1.7 Common Replication Administration Tasks
17.2 Replication Implementation
17.2.1 Replication Formats
17.2.2 Replication Channels
17.2.3 Replication Threads
17.2.4 Relay Log and Replication Metadata Repositories
17.2.5 How Servers Evaluate Replication Filtering Rules
17.3 Replication Security
17.3.1 Setting Up Replication to Use Encrypted Connections
17.3.2 Encrypting Binary Log Files and Relay Log Files
17.3.3 Replication Privilege Checks
17.4 Replication Solutions
17.4.1 Using Replication for Backups
17.4.2 Handling an Unexpected Halt of a Replica
17.4.3 Monitoring Row-based Replication
17.4.4 Using Replication with Different Source and Replica Storage Engines
17.4.5 Using Replication for Scale-Out
17.4.6 Replicating Different Databases to Different Replicas
17.4.7 Improving Replication Performance
17.4.8 Switching Sources During Failover
17.4.9 Switching Sources and Replicas with Asynchronous Connection Failover
17.4.10 Semisynchronous Replication
17.4.11 Delayed Replication
17.5 Replication Notes and Tips
17.5.1 Replication Features and Issues
17.5.2 Replication Compatibility Between MySQL Versions
17.5.3 Upgrading a Replication Topology
17.5.4 Troubleshooting Replication
17.5.5 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 17.4, “Replication Solutions”.

MySQL 8.2 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 17.1.3, “Replication with Global Transaction Identifiers”. For information on using binary log file position based replication, see Section 17.1, “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 23, MySQL NDB Cluster 8.2). In MySQL 8.2, 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 17.4.10, “Semisynchronous Replication”. MySQL 8.2 also supports delayed replication such that a replica deliberately lags behind the source by at least a specified amount of time; see Section 17.4.11, “Delayed Replication”. For scenarios where synchronous replication is required, use NDB Cluster (see Chapter 23, MySQL NDB Cluster 8.2).

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 17.1.2, “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 17.2.1, “Replication Formats”.

Replication is controlled through a number of different options and variables. For more information, see Section 17.1.6, “Replication and Binary Logging Options and Variables”. Additional security measures can be applied to a replication topology, as described in Section 17.3, “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 17.4, “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 17.5, “Replication Notes and Tips”. For answers to some questions often asked by those who are new to MySQL Replication, see Section A.14, “MySQL 8.2 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 17.2, “Replication Implementation”.