Prioritized Replication

Prioritized replication can be used when there is a strong business requirement to have tighter consistency for replicated data on specific attributes. In previous versions of Directory Server, updates were replicated in the order in which they were received. With prioritized replication, you can specify that updates to certain attributes take precedence when they are replicated to other servers in the topology.

Priority is a boolean feature, it is on or off. There are no levels of priority. In a queue of updates waiting to be replicated, updates with priority are replicated before updates without priority.

Priority rules are configured with the following replication priority rule properties:

• The identity of the client, bind-dn.

• The type of update, op-tyupe.

• The entry or subtree that was updated, base-dn.

• The attributes changed by the update, att.

For information about these properties, see repl-priority(5dsconf).

When the master replicates an update to one or more hubs or consumer replicas, the priority of the update is the same across all of the hubs and consumer replicas. If one parameter is configured in a priority rule for prioritized replication, all updates that match that parameter are prioritized for replication. If two or more parameters are configured in a priority rule for prioritized replication, all updates that match all parameters are prioritized for replication.

In the following scenario, it is possible that a master replica attempts to replicate an update to an entry before it has replicated the addition of the entry:

• The entry is added on the master replica and then updated on the master replica

• The update operation has replication priority but the add operation does not have replication priority

In this scenario, the update operation cannot be replicated until the add operation is replicated. The update waits for its chronological turn, after the add operation, to be replicated.

Prioritized replication provides the following benefits:

• Improved security. Prioritized replication is used by default for account lockout. Imagine for example that an employee leaves your organization, and you lock the employee's account. To ensure that the employee cannot log in to a remote server to which the account lockout has not been replicated, account lockout changes are replicated before other changes are replicated.

• Improved consistency. Directory Server replication is loosely consistent. With prioritized replication, you can assure stronger consistency for certain attributes that are considered important in your organization.