Managing Indexes; About Indexes; About Index Types - Red Hat DIRECTORY SERVER 8.0 - ADMINISTRATION Administration Manual

Chapter 10.

Managing Indexes

Indexing makes searching for and retrieving information easier by classifying and organizing attributes
or values. This chapter describes the searching algorithm itself, placing indexing mechanisms in
context, and then describes how to create, delete, and manage indexes.

10.1. About Indexes

This section provides an overview of indexing in Directory Server. It contains the following topics:
Section 10.1.1, "About Index Types"
•
Section 10.1.2, "About Default, System, and Standard Indexes"
•
Section 10.1.3, "Overview of the Searching Algorithm"
•
Section 10.1.5, "Balancing the Benefits of Indexing"
•

10.1.1. About Index Types

Indexes are stored in files in the directory's databases. The names of the files are based on the
indexed attribute, not the type of index contained in the file. Each index file may contain multiple
types of indexes if multiple indexes are maintained for the specific attribute. For example, all indexes
maintained for the common name attribute are contained in the cn.db4 file.
Directory Server supports the following types of index:
• Presence index (pres) contains a list of the entries that contain a particular attribute, which is very
useful for searched. For example, it makes it easy to examine any entries that contain access
control information. Generating an aci.db4 file that includes a presence index efficiently performs
the search for ACI=* to generate the access control list for the server.
The presence index is not used for base object searches.
• Equality index (eq) improves searches for entries containing a specific attribute value. For example,
an equality index on the cn attribute allows a user to perform the search for cn=Babs Jensen far
more efficiently.
• Approximate index (approx) is used for efficient approximate or sounds-like searches. For example,
an entry may include the attribute value cn=Robert E Lee. An approximate search would
return this value for searches against cn~=Robert Lee, cn~=Robert, or cn~=Lee. Similarly, a
search against l~=San Fransisco (note the misspelling) would return entries including l=San
Francisco.
• Substring index (sub) is a costly index to maintain, but it allows efficient searching against
substrings within entries. Substring indexes are limited to a minimum of three characters for each
entry.
For example, searches of the form cn=*derson , match the common names containing strings
such as Bill Anderson, Jill Henderson, or Steve Sanderson. Similarly, the search for
telephonenumber= *555* returns all the entries in the directory with telephone numbers that
contain 555.
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