Master-Master Replication

Master-master replication, also known as bidirectional replication, is a setup in which two or more databases are configured as master databases, and each master can accept write operations. This means that changes made to any master database are replicated to all other master databases in the configuration.

• In master-master replication, communication occurs bidirectionally between the master databases.
• When a write operation is performed on one master database, that change is replicated to all other master databases.
• If conflicting writes occur on different master databases, conflict resolution mechanisms are needed to ensure data consistency.

2.1. How Master-Master Replication generally works

In master-master replication, communication occurs bidirectionally between the master nodes. Each master node is responsible for accepting write operations and replicating these writes to the other master nodes in the system. The communication process typically involves the following steps:

• Write Operations: When a write operation (such as an insert, update, or delete) is performed on one master node, that node records the change in its transaction log.
• Replication Process: The master node has a replication process or thread that reads the transaction log and sends the changes (or updates) to the other master nodes.
• Network Communication: The changes are transmitted over the network from one master node to the other master nodes. This communication can be synchronous or asynchronous, depending on the configuration.
• Applying Changes: Upon receiving the changes, each master node applies them to its own copy of the data. The nodes may also have replication processes or threads that manage this process.
• Conflict Resolution: In cases where conflicting writes occur (i.e., the same data is modified on different master nodes simultaneously), conflict resolution mechanisms are needed to ensure data consistency. This can involve choosing one version of the data as the “winner” or merging conflicting changes.
• Acknowledgment: Once the changes are applied, each master node sends an acknowledgment back to the originating node to confirm that the changes have been received and applied successfully.

2.2 Real-World Analogy of Master-Master Replication

Imagine two highly trained air traffic controllers managing air traffic in a busy airspace

• Each controller has a designated sector and full authority to direct planes within their zone.
• They constantly communicate and share information to ensure flight paths don’t conflict, maintaining overall airspace safety.
• If one controller becomes unavailable, the other can seamlessly take over responsibility for both sectors, guaranteeing uninterrupted traffic flow.

2.3 Applications of Master-Master Replication

Below are the applications of Master-Master Replication:

• Multi-Datacenter Applications: Utilizing master-master replication for active-active configurations across different data centers, providing low-latency access to data.
• Collaborative Editing Platforms: Allowing users to concurrently edit documents by syncing changes between multiple master servers.

2.4. Benefits of Master-Master Replication

Below are the benefits of Master-Master Replication:

• Improved Write Scalability: Since write operations can be distributed among multiple master databases, the overall write performance of the system can be improved, especially in write-heavy applications.
• High Availability: If one master database fails, the other master databases can continue to accept write operations, ensuring that the system remains available.
• Load Balancing: Similar to master-slave replication, master-master replication allows for load balancing by distributing read and write operations among multiple databases.
• Data Locality: Master-master replication can be used to bring data closer to where it is being used, reducing latency and improving performance for users accessing the data.

2.5. Challenges of Master-Master Replication:

Below are the challenges of Master-Master Replication:

• Complexity: Setting up and managing master-master replication can be complex, especially when dealing with issues such as conflict resolution, data consistency, and network configuration.
• Conflict Resolution: Conflicts can arise if the same data is modified on different master nodes simultaneously. Implementing conflict resolution mechanisms can be challenging and may require manual intervention in some cases.
• Single Point of Failure: While master-master replication can improve availability by allowing multiple master nodes to accept write operations, it also introduces the risk of a single point of failure if all master nodes are in the same cluster or data center.

Database replication is like making copies of your important documents so you have backups in case something happens to the original. There are different ways to make these copies, like having one main copy (master) that gets updated and then making copies (slaves) of that updated version. Another way is to have multiple main copies (masters) that can all be updated and share those updates. In this article, we will see different types of database replication.

Let’s understand the types of database replication: