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Chapter 1. Defining a default index that applies to all newly created databases

The default index in Directory Server defines a set of attributes to be indexed. When you create a new database, Directory Server copies the default index attributes from cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config entry to the database-specific cn=index,cn=database_name,cn=ldbm database,cn=plugins,cn=config entry.

Note

Directory Server does not apply changes in the default index to existing databases.

1.1. 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.

1.2. 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 1.1. 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.

Important

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.

1.3. 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://server.example.com -b "cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config" -s one -o ldif-wrap=no
Table 1.1. Directory Server default index attributes

aci

cn

entryUSN

entryUUID

givenName

mail

mailAlternateAddress

mailHost

member

memberOf

nsUniqueId

nsCertSubjectDN

nsTombstoneCSN

ntUniqueId

ntUserDomainId

numSubordinates

objectClass

owner

parentId

seeAlso

sn

targetUniqueId

telephoneNumber

uid

uniqueMember

  
Warning

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

1.4. Maintaining the default index

Directory Server stores the default index attributes in the cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config entry. Note that you can only maintain the default index attributes using LDIF statements.

Procedure

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

    # ldapadd -D "cn=Directory Manager" -W -H ldap://server.example.com -x

dn: cn=roomNumber,cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config
objectClass: nsIndex
objectClass: top
cn: roomNumber
nsSystemIndex: false
nsIndexType: eq
nsIndexType: sub

    Explanation of the LDIF statement:

    • objectClass: nsIndex: Defines that this entry is an index entry.
    • objectClass: top: This object class is additionally required in index entries.
    • cn: Sets the name of the attribute to index.
    • nsSystemIndex: Indicates whether or not the index is essential to Directory Server operations.
    • nsIndexType: This multi-value attribute specifies the index types.

  • For example, to add the pres index type to the default index attributes of the roomNumber attribute, enter: 

    # ldapmodify -D "cn=Directory Manager" -W -H ldap://server.example.com -x

dn: cn=roomNumber,cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config
changetype: modify
add: nsIndexType
nsIndexType: pres

  • For example, to remove the pres index type from the default index attributes of the roomNumber attribute, enter: 

    # ldapmodify -D "cn=Directory Manager" -W -H ldap://server.example.com -x

dn: cn=roomNumber,cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config
changetype: modify
delete: nsIndexType
nsIndexType: pres

  • For example, to remove the roomNumber attribute from the default index, enter: 

    # ldapdelete -D "cn=Directory Manager" -W -H ldap://server.example.com -x cn=roomNumber,cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config

Verification

  • List the default index attributes to verify your changes: 

    # ldapsearch -H ldap://server.example.com:389 -D "cn=Directory Manager" -W -b "cn=default indexes,cn=config,cn=ldbm database,cn=plugins,cn=config" -x -s one -o ldif-wrap=no
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