HP-UX Directory Server Administrator Guide HP-UX Directory Server Version 8.1 (5900-3098, May 2013)

8.1.1 What directory units are replicated
The smallest unit of the directory that can be replicated is a database. This means that one can
replicate an entire database but not a subtree within a database. Therefore, when creating the
directory tree, consider any replication plans as part of determining how to distribute information.
Replication also requires that one database correspond to one suffix. This means that a suffix (or
namespace) that is distributed over two or more databases using custom distribution logic cannot
be replicated. For more information on this topic, see “Creating and Maintaining Databases” (page
38).
8.1.2 Read-write and read-only replicas
A database that participates in replication is called a replica. There are two kinds of replicas:
read-write or read-only:
• A read-write replica contains master copies of directory information and can be updated.
• A read-only replica services read, search, and compare requests, but refers all update
operations to read-write replicas.
A server can hold any number of read-only or read-write replicas.
8.1.3 Suppliers and consumers
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, with two exceptions:
• In the case of cascading replication, the hub server holds a read-only replica that it supplies
to consumers. “Cascading replication” (page 323) has more information.
• In the case of multi-master replication, the masters are both suppliers and consumers for the
same information. For more information, see “Multi-master replication” (page 321).
Replication is always initiated by the supplier server, never by the consumer (supplier-initiated
replication). Supplier-initiated replication allows a supplier server to be configured to push data
to multiple consumer servers.
8.1.4 Changelog
Every supplier server maintains a changelog, a record of all changes that a supplier or hub needs
to send to its consumers. A changelog is a special kind of database that describes the modifications
that have occurred on a replica. The supplier server then replays these modifications to the replicas
stored on consumer servers or to other suppliers, in the case of multi-master replication.
When an entry is modified, a change record describing the LDAP operation that was performed
is recorded in the changelog.
In Directory Server, the changelog is only intended for internal use by the server. For other
applications to read the changelog, use the Retro Changelog Plug-in, as described in “Using the
Retro changelog plug-in” (page 381).
8.1.5 Replication identity
When replication occurs between two servers, the replication process uses a special entry, called
the replication manager entry, to identify replication protocol exchanges and to control access to
the directory data. The replication manager entry, or any entry used during replication, must meet
the following criteria:
• It is created on the consumer server (or hub) and not on the supplier server.
• Create this entry on every server that receives updates from another server, meaning on every
hub or dedicated consumer.
318 Managing Replication