About Directory Replication

This section briefly introduces some of the basic concepts of replication. The other sections in this chapter explain these concepts in further detail.

Replication is the process of copying and maintaining the same naming contexts on multiple directory servers. It improves performance by providing more servers to handle queries, and reliability by eliminating risks associated with a single point of failure.

Replication can be either full or partial.

Full replication involves propagating the entire DIT to another node.

Partial replication involves propagating one or more subtrees, rather than the entire DIT, to another node.

The directory servers that participate in the replication of a given naming context form what is called a directory replication group (DRG). The relationship among the directory servers in a DRG is represented on each node by a special directory entry called a replication agreement.

Each copy of a naming context contained within a server is called a replica. Replicas can be read-only, updatable, or both. Servers that hold updatable replicas are called suppliers. Their changes are propagated to other servers called consumers.

A directory replication group can be either single-master, multimaster, or fan-out.

A single-master replication group has only one supplier replicating changes to one or more consumers. Only the supplier can be updated, and consumers are read-only.

Multimaster replication, also called peer-to-peer or n-way replication, enables multiple sites, acting as equals, to manage groups of replicated data. In a multimaster replication environment, each node is both a supplier and a consumer node, and the entire directory is replicated on each node.

A fan-out replication group, also called a point-to-point replication group, has a supplier replicating directly to a consumer. That consumer can then replicate to one or more other consumers. The replication can be either full or partial.

In a directory replication group, the protocol for transferring data between nodes can be based on either Oracle9i Advanced Replication or LDAP.