What’s Multi-Master Replication?

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Multi-master replication is a technique employed by database management software so that multiple copies of a single database stored on different computers can be used and updated by many users in a decentralized manner. When a change is made to a database that uses multimaster replication, the change is broadcast to all other computers on the network so that all copies of the database in use are updated. Some benefits of a multi-master replication setup include redundant data backups and a decentralized architecture where updates to copies of a database can be maintained even if one of the computers on the network goes down. Without a single assigned master system, as is the case in the master-slave architecture, changes and administrative commands to control the database can be issued from any multi-master terminal within the network instead of relying on just one physical terminal. The biggest complication that can occur with using a multimaster replication system involves updating all systems fast enough so that data stays in sync at all times across the network.

The term “multi-master” comes from the most basic method of master-slave replication, where a single terminal is designated as the master. In a master-slave situation, only a single master is able to update information about the slave drives. A multi-master replication system has multiple systems designated as masters, and each master might be responsible only for itself, or it might be responsible for a number of computers known as a replication group. With multiple masters, any master system can initiate a change to all other master systems, potentially leading to very complex network interactions in very large systems.

There are two forms of multimaster replication, the first of which is synchronous replication. Synchronous replication works by updating all copies of a database in real time whenever a change is made. This eliminates most of the situations that can arise when data is out of sync across the network, but creates a huge amount of network traffic and may require a large amount of processing power to implement in a larger system. For these reasons, synchronous replication is primarily used in networks where there are only a handful of master computers.

The second type of multimaster replication is asynchronous replication. Instead of updating systems every time a change is made, changes to a database are stored as events on each system and those changes are applied when an event is triggered or during scheduled update periods. This means that less network bandwidth and processing power is used, but increases the chances that two users could attempt to change the same information in conflicting ways due to update delay or latency. Most distributed database management systems use asynchronous replication due to the low amount of resources consumed compared to synchronous multimaster replication.

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