Chapter 2. Maintaining the indexes of a specific database

Each database in Directory Server has its own index. You can create, update, and delete indexes using the dsconf utility or the web console.

2.1. The different index types

Directory Server stores the indexes of each indexed attribute in a separate database file in the instance’s database directory. For example, the indexes of the sn attribute are stored in the /var/lib/dirsrv/slapd-instance_name/db/database_name/sn.db file. Each index file can contain multiple index types if Directory Server maintains different indexes for an attribute.

Directory Server supports the following index types:

  • The presence index (pres) is a list of the entries that contain a particular attribute. For example, use this type when clients frequently perform searches, such as attribute=mail.
  • The equality index (eq) improves searches for entries containing a specific attribute value. For example, an equality index on the cn attribute enables faster searches for cn=first_name last_name.
  • The approximate index (approx) enables efficient approximate or sounds-like searches. For example, searches for cn~=first_name last_name, cn~=first_name, or cn~=first_nam (note the misspelling) would return an entry cn=first_name X last_name. Note that the metaphone phonetic algorithm in Directory Server supports only US-ASCII letters. Therefore, use approximate indexing only with English values.
  • The substring index (sub) is a costly index to maintain, but it enables efficient searching against substrings within entries. Substring indexes are limited to a minimum of three characters for each entry. For example, searches for telephoneNumber=*555* return all entries in the directory with a value that contains 555 in the telephoneNumber attribute.
  • International index speeds up searches for information in international directories. The process for creating an international index is similar to the process for creating regular indexes, except that it applies a matching rule by associating an object identifier (OID) with the attributes to be indexed.

2.2. Balancing the benefits of indexing

Before you create new indexes, balance the benefits of maintaining indexes against the costs:

  • Approximate indexes are not efficient for attributes commonly containing numbers, such as phone numbers.
  • Substring indexes do not work for binary attributes.
  • Avoid equality indexes on attributes that contain big values, such as an image.
  • Maintaining indexes for attributes that are not commonly used in searches increases the overhead without improving the search performance.
  • Attributes that are not indexed can still be used in search requests, although the search performance can be degraded significantly, depending on the type of search.

Indexes can become very time-consuming. For example, if Directory Server receives an add operation, the server examines the indexing attributes to determine whether an index is maintained for the attribute values. If the created attribute values are indexed, Directory Server adds the new attribute values to the index, and then the actual attribute values are created in the entry.

Example 2.1. Indexing steps Directory Server performs when a user adds an entry

Assume that Directory Server maintains the following indexes:

  • Equality, approximate, and substring indexes for the cn and sn attributes.
  • Equality and substring indexes for the telephoneNumber attribute.
  • Substring indexes for the description attribute.

For example, a user adds the following entry:

dn: cn=John Doe,ou=People,dc=example,dc=com
objectclass: top
objectClass: person
objectClass: orgperson
objectClass: inetorgperson
cn: John Doe
cn: John
sn: Doe
ou: Manufacturing
ou: people
telephoneNumber: 408 555 8834
description: Manufacturing lead

When the user adds the entry, Directory Server performs the following steps:

  1. Create the cn equality index entry for John and John Doe.
  2. Create the cn approximate index entries for John and John Doe.
  3. Create the cn substring index entries for John and John Doe.
  4. Create the sn equality index entry for Doe.
  5. Create the sn approximate index entry for Doe.
  6. Create the sn substring index entry for Doe.
  7. Create the telephoneNumber equality index entry for 408 555 8834.
  8. Create the telephoneNumber substring index entry for 408 555 8834.
  9. Create the description substring index entry for Manufacturing lead.

This example illustrates that the number of actions required to create and maintain databases for a large directory can be very resource-intensive.


Do not define a substring index for membership attributes (for example, member,uniquemember) because it can impact Directory Server performance. When adding or removing members, for example,uniquemember to a group with many members, the computation of the uniquemember substring index requires to evaluating all uniquemember values and not only added or removed values.

2.3. Default index attributes

Directory Server stores the default index attributes in the cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config entry. To display them, including their index types, enter:

# ldapsearch -D "cn=Directory Manager" -W -H ldap:// -b "cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config" -s one -o ldif-wrap=no

Table 2.1. Directory Server default index attributes



























Removing the attributes listed in the table (system indexes) from the index of databases can significantly affect the Directory Server performance.

2.4. Maintaining the indexes of a specific database using the command line

You can use the dsconf utility to maintain index settings using the command line.


  • For example, to add the roomNumber attribute to the index of the userRoot database with the index types eq and sub, enter:

    # dsconf -D "cn=Directory Manager" ldap:// backend index add --attr roomNumber --index-type eq --index-type sub --reindex userRoot

    The --reindex option causes that Directory Server automatically re-indexes the database.

  • For example, to add the pres index type to the index settings of the roomNumber attribute in the userRoot database, enter:

    # dsconf -D "cn=Directory Manager" ldap:// backend index set --attr roomNumber --add-type pres userRoot
  • For example, to remove the pres index type from the index settings of the roomNumber attribute in the userRoot database, enter:

    # dsconf -D "cn=Directory Manager" ldap:// backend index set --attr roomNumber --del-type pres userRoot
  • For example, to remove the roomNumber attribute from the index in the userRoot database, enter:

    # dsconf -D "cn=Directory Manager" ldap:// backend index delete --attr roomNumber userRoot


  • List the index settings of the userRoot database:

    # dsconf -D "cn=Directory Manager" ldap:// backend index list userRoot

2.5. Recreating an index while the instance offline

You can use the dsctl db2index utility for reindexing the whole database while the instance is offline.


  • You created an indexing entry or added additional index types to the existing userRoot database.


  1. Shut down the instance:

    # dsctl instance_name stop
  2. Recreate the index:

    1. For all indexes in the database, run:

      # dsctl instance_name db2index
      [23/Feb/2023:05:38:28.034826108 -0500] - INFO - check_and_set_import_cache - pagesize: 4096, available bytes 1384095744, process usage 27467776
      [23/Feb/2023:05:38:28.037952026 -0500] - INFO - check_and_set_import_cache - Import allocates 540662KB import cache.
      [23/Feb/2023:05:38:28.055104135 -0500] - INFO - bdb_db2index - userroot: Indexing attribute: aci
      [23/Feb/2023:05:38:28.134350191 -0500] - INFO - bdb_db2index - userroot: Finished indexing.
      [23/Feb/2023:05:38:28.151907852 -0500] - INFO - bdb_pre_close - All database threads now stopped
      db2index successful
    2. For specific attribute indexes, run:

      # dsctl instance_name db2index userRoot --attr aci cn givenname

      The following command recreates indexes for aci, cn, and givenname attributes.

    3. For more information regarding dsctl (offline) command, run:

      # dsctl instance_name db2index --help
  3. Start the instance:

    # dsctl instance_name start


  • List the index settings of the userRoot database:

    # dsconf -D "cn=Directory Manager" ldap:// backend index list userRoot

2.6. Maintaining the indexes of a specific database using the web console

You can use the web console to maintain index settings in Directory Server.


  • You are logged in to the instance in the web console.


  • Navigate to DatabaseSuffixessuffix_nameIndexesDatabase Indexes.

    • To add an attribute to the index:

      • Click Add Index.
      • Enter the attribute name to the Select An Attribute field.
      • Select the index types.
      • Select Index attribute after creation.
      • Click Create Index.
    • To update the index settings of an attribute:

      • Click the overflow menu next to the attribute, and select Edit Index.
      • Update the index settings to your needs.
      • Select Index attribute after creation.
      • Click Save Index.
    • To delete an attribute from the index:

      • Click the overflow menu next to the attribute, and select Delete Index.
      • Select Yes, I am sure, and click Delete.
      • In the Suffix Tasks menu, select Reindex Suffix.


  • Navigate to DatabaseSuffixessuffix_nameIndexesDatabase Indexes, and verify that the index settings reflect the changes you made.