Overview Of Directory Index Types; Evaluating The Costs Of Indexing - Red Hat DIRECTORY SERVER 8.1 - DEPLOYMENT Deployment Manual

Chapter 5. Designing the Directory Topology
file for a particular attribute can contain multiple types of indexes, so several types of index can be
maintained for each attribute. For example, a file called cn.db4 contains all of the indexes for the
common name attribute.
Different types of indexes are used depending on the types of applications that use the directory
service. Different applications may frequently search for a particular attribute, or may search the
directory in a different language, or may require data in a particular format.

5.4.1. Overview of Directory Index Types

Directory Server supports the following types of index:
• Presence index — Lists entries that possess a particular attribute, such as uid.
• Equality index — Lists entries that contain a specific attribute value, such as cn=Babs Jensen.
• Approximate index — Allows approximate (or "sounds-like") searches. For example, an entry might
contain the attribute value of cn=Babs L. Jensen. An approximate search would return this value
for searches against cn~=Babs Jensen, cn~=Babs, and cn~=Jensen.
NOTE
Approximate indexes require that names be written in English using ASCII characters.
• Substring index — Allows searches against substrings within entries. For example, a search for
cn=*derson would match common names containing this string (such as Bill Anderson, Norma
Henderson, and Steve Sanderson).
• International index — Improves the performance of searches for information in international
directories. Configure the index to apply a matching rule by associating a locale (internationalization
OID) with the attribute being indexed.
• Browsing index or virtual list view (VLV) index — Improves the display performance of entries in the
Directory Server Console. A browsing index can be created on any branch in the directory tree to
improve the display performance.

5.4.2. Evaluating the Costs of Indexing

Indexes improve search performance in the directory databases, but there is a cost involved:
• Indexes increase the time it takes to modify entries.
The more indexes being maintained, the longer it takes the directory service to update the database.
• Index files use disk space.
The more attributes being indexed, the more files are created. If there are approximate and
substring indexes for attributes that contain long strings, these files can grow rapidly.
• Index files use memory.
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