Replication Resource Requirements - Red Hat DIRECTORY SERVER 8.1 - DEPLOYMENT Deployment Manual

Chapter 6. Designing the Replication Process
Fractional replication is enabled and configured per replication agreement. The exclusion of attributes
is applied equally to all entries. As far as the consumer server is concerned, the excluded attributes
always have no value. Therefore, a client performing a search against the consumer server never
sees the excluded attributes. Similarly, should it perform a search that specifies those attributes in its
filter, no entries match.
Fractional replication is particularly useful in the following situations:
• Where the consumer server is connected via a slow network, excluding infrequently changed
attributes or larger attributes such as jpegPhoto results in less network traffic.
• Where the consumer server is placed on an untrusted network such as the public Internet, excluding
sensitive attributes such as telephone numbers provides an extra level of protection that guarantees
no access to those attributes even if the server's access control measures are defeated or the
machine is compromised by an attacker.
Configuring fractional replication is described in the replication agreement and supplier configuration
sections in chapter 8, "Managing Replication," in the Administrator's Guide.

6.3.3. Replication Resource Requirements

Using replication requires more resources. Consider the following resource requirements when
defining the replication strategy:
• Disk usage — On supplier servers, the changelog is written after each update operation. Supplier
servers that receive many update operations may experience higher disk usage.
NOTE
Each supplier server uses a single changelog. If a supplier contains multiple replicated
databases, the changelog is used more frequently, and the disk usage is even higher.
• Server threads — Each replication agreement consumes one server thread. So, the number of
threads available to client applications is reduced, possibly affecting the server performance for the
client applications.
• File descriptors — The number of file descriptors available to the server is reduced by the
changelog (one file descriptor) and each replication agreement (one file descriptor per agreement).
6.3.4. Managing Disk Space Required for Multi-Master Replication
Multi-master replicas maintain additional logs, including the changelog of directory edits, state
information for update entries, and tombstone entries for deleted entries. This information is required
for multi-master replication to be performed. Because these log files can get very large, periodically
cleaning up these files is necessary to keep from wasting disk space.
There are four attributes which can configure the changelog maintenance for the multi-master replica.
Two are under cn=changelog5 and relate directly to trimming the changelog:
• nsslapd-changelogmaxage sets the maximum age that the entries in the changelog can
be; once an entry is older than that limit, it is deleted. This keeps the changelog from growing
indefinitely.
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