It is not required for all domain controllers to replicate with each other domain controller as this would cause excessive network traffic in large Active Directory deployments.
Multi-master replication is a method of database replication which allows data to be stored by a group of computers, and updated by any member of the group. The multi-master replication system is responsible for propagating the data modifications made by each member to the rest of the group, and resolving any conflicts that might arise between concurrent changes made by different members.Multi-master replication can be contrasted with master-slave replication, in which a single member of the group is designated as the "master" for a given piece of data and is the only node allowed to modify that data item.Some Active Directory needs are however better served by Flexible single master operation. Open DS (and its successor product Open DJ) implemented multi-master since version 1.0.The Open DS/Open DJ multi-master replication is asynchronous, it uses a log with a publish-subscribe mechanism that allows scaling to a large number of nodes.The widely used open source LDAP server implements multi-master replication since its version 2.4 (October 2007) .
Apache Couch DB uses a simple, HTTP-based multi-master replication system built from its use of an append only data-store and use of Multiversion Concurrency Control (MVCC) Each document contains a (revision ID), so every record stores the evolutionary timeline of all previous revision IDs leading up to itself—which provides the foundation of Couch DB's MVCC system.Multi-master replication can also be contrasted with failover clustering where passive slave servers are replicating the master data in order to prepare for takeover in the event that the master stops functioning.The master is the only server active for client interaction.My SQL: My SQL Group Replication, a plugin for virtual synchronous multi master with conflict handling and distributed recovery was released with 5.7.17.Cluster Projects: My SQL Cluster supports conflict detection and resolution between multiple masters since version 6.3 for true multi-master capability for the My SQL Server.Synchronous multi-master replication uses Oracle's two phase commit functionality to ensure that all databases with the cluster have a consistent dataset.