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Unit of Replication
The smallest unit of replication is a database. This means that you can replicate an
entire database but not a subtree within a database. Therefore, when you create
your directory tree, you must take your replication plans into consideration. For
more information on how to set up your directory tree, refer to chapter 4,
"Designing the Directory Tree," on page 61."
The replication mechanism also requires that one database correspond to one
suffix. This means that you cannot replicate a suffix (or namespace) that is
distributed over two or more databases.
Read-Write Replica/Read-Only Replica
A database that participates in replication is defined as a replica. There are two
kinds of replicas: read-write or read-only. The read-write replicas contain master
copies of directory information and can be updated. Read-only replicas refer all
update operations to read-write replicas.
Supplier/Consumer
A server that holds a replica that is copied to a replica on a different server is called
a supplier for that replica. A server that holds a replica that is copied from a
different server is called a consumer for that replica. Generally, the replica on the
supplier server is a read-write replica, and the one on the consumer server is a
read-only replica. There are exceptions to this statement:
•
In the case of cascading replication, the hub supplier holds a read-only replica
that it supplies to consumers. For more information, refer to "Cascading
Replication," on page 121.
•
In the case of multi-master replication, the suppliers are suppliers and
consumers for the same read-write replica. For more information, refer to
"Multi-Master Replication," on page 117.
NOTE
Replication is always initiated by the supplier server, never by the
consumer, unlike earlier versions of the Directory Server that
allowed consumer-initiated replication (where consumer servers
could retrieve data from a supplier server).
For any particular replica, the supplier server must:
•
Respond to read requests and update requests from directory clients.
•
Maintain state information and a changelog for the replica.
Introduction to Replication
Chapter 6
Designing the Replication Process
113
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