15.18. Trimming the Replication Changelog

The Directory Server changelog maintains a list of received and processed changes. It includes client changes and changes received from replication partners.
By default, Directory Server trims the changelog entries that are more than seven days old. However, you can modify this and configure:
  • A maximum age of entries in the changelog in the nsslapd-changelogmaxage parameter.
  • The total number of records in the changelog in the nsslapd-changelogmaxentries parameter.
If you enabled at least one of these settings, Directory Server trims the changelog every 5 minutes by default (nsslapd-changelogtrim-interval).
All records and records created subsequently remain in the changelog until it is successfully replicated on all servers in the topology. If you must remove the supplier from the topology as described in Section 15.10.2, “Removing a Supplier from the Replication Topology”, then Directory Server trims all the updates of this supplier from changelogs on other servers.

15.18.1. Configuring Replication Changelog Trimming

By default, Directory Server trims the changelog entries that are more than seven days old. However, you can configure the time after which Directory Server can remove entries. You can also configure Directory Server to remove entries automatically when the number of entries exceeds a configured value.

Note

Red Hat recommends setting a maximum age instead of a maximum number of entries. The maximum age should match the replication purge delay set in the nsDS5ReplicaPurgeDelay parameter in the cn=replica,cn=suffixDN,cn=mapping tree,cn=config entry.
Perform this procedure on the supplier:
  1. Configure change log trimming:
    • To set a maximum age of changelog entries, enter: 
      # dsconf -D "cn=Directory Manager" ldap://server.example.com replication set-changelog --max-age "4w"
      This command sets the maximum age to four weeks. The parameter supports the following units:
      • s (S) for seconds
      • m (S) for minutes
      • h (H) for hours
      • d (D) for days
      • w (W) for weeks
    • To set a maximum number of entries, enter: 
      # dsconf -D "cn=Directory Manager" ldap://server.example.com replication set-changelog --max-entries "100000"
      This command sets the maximum number of entries in the changelog to 100,000.
  2. By default, Directory Server trims the changelog every 5 minutes (300 seconds). To set a different interval, enter: 
    # dsconf -D "cn=Directory Manager" ldap://server.example.com replication set-changelog --trim-interval 600
    This command sets the interval to 10 minutes (600 seconds).

15.18.2. Manually Reducing the Size of a Large Changelog

In certain situations, such as if replication changelog trimming was not enabled, the changelog can grow to an excessively large size. To fix this, you can reduce the changelog size manually.
Perform this procedure on the supplier.

Prerequisites

You enabled replication.

Procedure

  1. Optional: Display the size of the changelog: 
    # ls -lh /var/lib/dirsrv/slapd-instance_name/changelogdb/
total 159M
rw------. 1 dirsrv dirsrv 159M  Nov 21 04:01 a1cf5703-697a11ed-896ed7a0-04f329b5_637b3daf000000010000.db
rw------. 1 dirsrv dirsrv 30 Nov 21 03:58 DBVERSION
    This example shows that the /var/lib/dirsrv/slapd-instance_name/changelogdb/ directory contains only one changelog file with the size of 159M.
  2. To be able to reset the parameters after reducing the changelog size, display and note the current values of the corresponding parameters: 
    # dsconf instance_name replication get-changelog
dn: cn=changelog5,cn=config
cn: changelog5
nsslapd-changelogdir: /var/lib/dirsrv/slapd-instance_name/changelogdb/
nsslapd-changelogmaxage: 7d
nsslapd-changelogtrim-interval: 300
objectClass: top
objectClass: nsChangelogConfig
    If you do not see any specific attributes in the output, Directory Server uses their default values.
  3. Temporarily, reduce trimming-related parameters: 
    # dsconf -D "cn=Directory Manager" ldap://server.example.com replication set-changelog --max-age "300s" --max-entries 500 --trim-interval 60

    Important

    For performance reasons, do not permanently use too short interval settings.
  4. Wait until the time set in the --trim-interval parameter expires.
  5. Compact the changelog to regain the disk space: 
    # dsconf -D "cn=Directory Manager" ldap://server.example.com backend compact-db --only-changelog
  6. Reset the changelog parameters to the values they had before you temporarily reduced them: 
    # dsconf -D "cn=Directory Manager" ldap://server.example.com replication set-changelog --max-age "7d" --max-entries 0 --trim-interval 300

Verification

  • Display the size of the changelog: 
    # ls -lh /var/lib/dirsrv/slapd-instance_name/changelogdb/

total 14M
rw------. 1 dirsrv dirsrv 14M Nov 21 05:08 a1cf5703-697a11ed-896ed7a0-04f329b5_637b3daf000000010000.db
rw------. 1 dirsrv dirsrv 30 Nov 21 05:01 DBVERSION