A Beginners Guide to MySQL Replication Part 1: Introduction to MySQL Replication

This article is part of Aisha Bukar's 6 part series: A Beginners Guide to MySQL Replication. The entries include:

 MySQL Replication is a process where data from one MySQL database known as the source (formerly called “master”) is copied over to one or more other databases called replicas (formerly called “slaves”). Think of this like having a backup buddy that is always in sync and up to date, giving you peace of mind.

It’s important to highlight that in 2020, MySQL took the step to modernize its language by retiring outdated terms such as ‘master’ and ‘slave’ and replacing them with more inclusive language – ‘source’ and ‘replica’. The company is actively working towards updating its queries and documentation with these updated terms. According to the official blog post, the origin of these words is negative and does not fit the description.

Note that some of the syntax will still reference the old terms.

There are several benefits to using MySQL replication. For starters, it helps to increase the reliability and availability of your data. If the source database goes down, one of the replica databases can step in to take its place, keeping your application running smoothly. Plus, by distributing the load across multiple servers, replication can help to improve performance and prevent downtime. Another bonus? Replication makes it easier to back up and recover your data. So, if anything were to happen, you can rest easy knowing that you have a backup ready to go.

We have different types of replication setups, such as asynchronous, semi-synchronous, and synchronous replication. These are the standard replication types mentioned in the documentation. In this series, we’ll be delving into each of these replication types and examining their requirements, benefits, and limitations. So, hold on tight, as we embark on a journey of discovery to setting up and choosing the right replication method.

Types of MySQL Replication

The choice of replication method depends on the specific requirements of your application. There are various replication types available in MySQL, each having its pros and limitations:

Asynchronous replication:

This is a type of replication in MySQL that involves a single source server that receives all write operations and one or more replica servers that replicate the data from the source. This type of replication is useful for scaling read-only operations. The source server does not wait for acknowledgment from the replica servers before committing changes. Here are some of the benefits of asynchronous replication:

  • Scalability: Asynchronous replication allows you to scale out the number of replica servers to meet growing demands for read-only access to data.
  • Performance: Asynchronous replication allows the source server to commit changes to the database immediately, which can provide high performance as the source server does not need to wait for the replica servers to catch up.
  • Flexibility: Asynchronous replication allows you to locate replica servers in different geographic locations, providing access to data from multiple regions.

Potential Limitations: Asynchronous replication is a great solution for businesses looking to scale their read-only operations and ensure high scalability. However, it may not be the best fit for applications that require real-time updates and immediate consistency due to some of its downsides, such as:

  • Data consistency: Since the source server does not wait for the replica servers to catch up before committing changes, there may be a temporary loss of data in the event of a failure. This can result in a lack of consistency between the source and replica servers.
  • Recovery time: If a failure occurs on the source server, it may take longer to recover and restore data consistency as the replica servers may have lagged.
  • Lagging: Since the replica servers may not be in real-time sync with the source, there may be a lag in the replication process that can result in outdated data on the replica servers.

Synchronous Replication

This is a method of replicating data where the source server waits for acknowledgment from the replica servers before committing changes to the database. This ensures that data remains consistent across all servers and eliminates the risk of temporary data loss in the event of a failure. There are several benefits to using synchronous replication, some of which are:

  • Data consistency and reliability: One of the key benefits of synchronous replication is the high level of data consistency and reliability it provides. With this method, you can be confident that all servers in your environment have the same up-to-date information, even in the event of a failure.
  • Fast recovery time: It can provide a faster recovery time in the event of a failure, as the replica servers already have the latest data. This can be especially important in high-availability environments where you need to ensure minimal downtime.

Potential Limitations: However, just like for asynchronous, there are also some limitations to synchronous replication that you should be aware of, such as:

  • Low performance: Since the source server must wait for acknowledgment from the replica servers before committing changes. This can slow down the processing of updates and inserts, especially if the replica servers are located far away from the source server.
  • High complexity: Synchronous replication can be more complex to set up and manage than asynchronous replication, as it requires more coordination between the servers. The high level of consistency and reliability it provides also requires more resources, including network bandwidth and disk space, to ensure smooth operation.

Semi-synchronous replication

This is a replication method that offers a compromise between the high data consistency of synchronous replication and the improved performance of asynchronous replication. With semi-synchronous replication, the source server waits for at least one replica server to acknowledge the receipt of updates before committing changes to the database. Here’s why semi-synchronous replication is a game-changer:

  • Data consistency and performance: It provides a good balance between data consistency and performance. Since the source server only needs to wait for one replica server to acknowledge the receipt of updates, it can complete transactions more quickly than with synchronous replication, which requires all replica servers to acknowledge the receipt of updates.
  • Reduced data loss: It can help reduce the risk of data loss in the event of a failure. With this method, the replica server acts as a backup of the data, providing a level of protection against temporary data loss in the event of a source server failure.

Potential Limitations: Of course, like all good things in life, semi-synchronous replication comes with a few trade-offs.

  • It’s Not for the Faint of Heart: It can still be more complex to set up and manage than asynchronous replication, as it requires coordination between the source and replica servers.
  • Data consistency: If the replica server that acknowledges the receipt of updates experiences a failure, data consistency may be affected, as the source server will still commit changes to the database.

You can decide whether synchronous, asynchronous, or semi-synchronous replication is the best option for your environment with some thorough planning and taking into account the evaluation of your data demands and use cases.

Replication formats

MySQL supports two core types of replication formats. Let’s take a closer look at each of these formats to understand how they work and what their pros and cons are.

Statement-based replication: Statement-based replication works by recording changes to a database as SQL statements and then replicating those statements to all replicas. The replicas then execute the same statements in the same order as the primary database. SBR is an easy-to-use and efficient replication format that’s ideal for simple, straightforward replication scenarios.

However, it does have some limitations. For example, it may not handle certain types of non-deterministic statements well, which can cause problems during replication.

Row-based replication: Row-based replication records changes to a database as changes to individual rows of data. This type of replication is much more flexible and robust than SBR, as it can handle more complex changes to data and can resolve replication conflicts more easily. It’s also better equipped to handle complex data structures, making it a good choice for demanding replication scenarios.

However, RBR is also more resource intensive than SBR, as it requires more network bandwidth and storage space to transmit the additional data.

Requirements for setting up MySQL Replication

Replicating data from a source database to a replica database is a great way to improve the performance of your MySQL infrastructure. But before you dive into setting up replication, there are a few key requirements you need to be aware of:

  • MySQL Version: Ensure that both the source and replica servers are running the same version of MySQL. This will guarantee that data can be replicated between the two servers without any compatibility issues.
  • Network Connectivity: The source and replica servers need to be able to communicate with each other over a network. This can be achieved by having both servers on the same network, or by setting up a secure connection between them.
  • User Privileges: A user account is required for replication, and it must have sufficient privileges on both the source and replica servers. The user must have the `REPLICATION SLAVE` privilege on the source and the `REPLICATION CLIENT` privilege on the replica.
  • Binary Logging: Binary logging must be enabled on the source server. This is essential for the replica to receive updates to the database. In order to set up binary logging in MySQL replication, you need to modify the MySQL configuration file (my.cnf or my.ini) on the source server to enable binary logging.
  • Unique Server IDs: Each MySQL server must have a unique server ID. This allows you to keep track of which data is being replicated from where.
  • Source Database Backup: To initialize the replica, you need to create a backup of the source database. This can be done using the `mysqldump` utility (Lukas Vileikis recently blogged about this utility here).
  • Storage Space: Make sure that both the source and replica servers have enough storage space to accommodate the replicated data.


Phew, that was a lot to digest! MySQL replication is a complex topic, and it’s essential to have a solid grasp of the fundamentals before diving into the technical details. But don’t worry, because in Part 2 of this series, we’re diving deep into the heart of the matter and exploring the nitty-gritty details of the replication process. Get ready to flex your query-writing muscles and gain a deeper understanding of this powerful tool!