HP-UX Directory Server 8.1 deployment guide

For more information on how to set up the directory tree, see Chapter 4 “Designing the directory
tree”.
The replication mechanism also requires that one database correspond to one suffix. A suffix (or
namespace) that is distributed over two or more databases cannot be replicated.
6.1.1.2 Read-write and read-only replicas
A database that participates in replication is defined as a replica. Directory Server supports two
types of replicas: read-write and 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.
6.1.1.3 Suppliers and consumers
A server that stores a replica that is copied to a different server is called a supplier. A server that
stores a replica that is copied from a different server is called a consumer. Generally speaking,
the replica on the supplier server is a read-write replica; the replica on the consumer server is a
read-only replica. However, the following exceptions apply:
• In the case of cascading replication, the hub supplier holds a read-only replica that it supplies
to consumers. For more information, see “Cascading replication”.
• In the case of multi-master replication, the suppliers function as both suppliers and consumers
for the same read-write replica. For more information, see “Multi-master replication”.
NOTE:
In the current version of HP-UX Directory Server, replication is always initiated by the supplier
server, never by the consumer. This is unlike earlier versions of Directory Server, which allowed
consumer-initiated replication (where consumer servers could retrieve data from a supplier
server).
Suppliers 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.
• Initiate replication to consumer servers.
The supplier server is always responsible for recording the changes made to the read-write
replicas that it manages, so the supplier server makes sure that any changes are replicated to
consumer servers.
Consumers A consumer server must:
• Respond to read requests.
• Refer update requests to a supplier server for the replica.
Whenever a consumer server receives a request to add, delete, or change an entry, the request
is referred to a supplier for the replica. The supplier server performs the request, then replicates
the change.
Hub suppliers In the special case of cascading replication, the hub supplier must:
• Respond to read requests.
• Refer update requests to a supplier server for the replica.
• Initiate replication to consumer servers.
For more information on cascading replication, see “Cascading replication”.
6.1.1.4 Replication and changelogs
Every supplier server maintains a changelog. A changelog is a record of the modifications that
have occurred on a replica. The supplier server then replays these modifications on the replicas
stored on consumer servers, or on other suppliers in the case of multi-master replication.
74 Designing the replication process