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

7.2.1. Resource Requirements

Synchronization uses server resources. Consider the following resource requirements when defining
the replication strategy:
• Disk usage — The changelog is written after each update operation. Servers receiving many
update operations may see higher disk usage. In addition, a single changelog is maintained for all
replication databases and synchronized databases. If a supplier contains multiple replicated and
synchronized databases, the changelog is used more frequently, and the disk usage is even higher.
• Server threads — The synchronization agreement uses one server thread.
• File descriptors — The number of file descriptors available to the server is reduced by the
changelog (one file descriptor) and each replication and synchronization agreement (one file
descriptor per agreement).
• Quality of the LANs and WANs connecting different buildings or remote sites and the amount of
available bandwidth.
• The number and size of the entries stored in the directory.
A site that manages human resource databases or financial information is likely to put a heavier load
on the directory than a site containing engineering staff that uses the directory for simple telephone
book purposes.
7.2.2. Managing Disk Space for the Changelog
As with multi-master replications, synchronization requires a changelog of to track directory edits and
log entries for the state information for update entries, and tombstone entries for deleted entries. This
information is required for synchronization. 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 maintain the changelog. 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.
• nsslapd-changelogmaxentries sets the maximum number of entries that are allowed in
the changelog. Like nsslapd-changelogmaxage, this also trims the changelog, but be careful
about the setting. This must be large enough to allow a complete set of directory information or
synchronization may not function properly.
The other two attributes are under the synchronization agreement entry in cn=sync_agreement,
cn=WindowsReplica, cn="suffixDN", cn=mapping tree, cn=config. These two attributes
relate to maintenance information kept in the changelog, the tombstone and state information, rather
than the directory edits information.
• nsDS5ReplicaPurgeDelay sets the maximum age that tombstone (deleted) entries and state
information can be in the changelog. Once a tombstone or state information entry is older than
that age, it is deleted. This differs from the nsslapd-changelogmaxage attribute in that the
nsDS5ReplicaPurgeDelay value applies only to tombstone and state information entries;
nsslapd-changelogmaxage applies to every entry in the changelog, including directory
modifications.
Resource Requirements
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