Chapter 5. Designing the Directory Topology72file for a particular attribute can contain multiple types of indexes, so several types of index can bemaintained for each attribute. For example, a file called cn.db4 contains all of the indexes for thecommon name attribute.Different types of indexes are used depending on the types of applications that use the directoryservice. Different applications may frequently search for a particular attribute, or may search thedirectory in a different language, or may require data in a particular format.5.4.1. Overview of Directory Index TypesDirectory 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 mightcontain the attribute value of cn=Babs L. Jensen. An approximate search would return this valuefor searches against cn~=Babs Jensen, cn~=Babs, and cn~=Jensen.NOTEApproximate indexes require that names be written in English using ASCII characters.• Substring index — Allows searches against substrings within entries. For example, a search forcn=*derson would match common names containing this string (such as Bill Anderson, NormaHenderson, and Steve Sanderson).• International index — Improves the performance of searches for information in internationaldirectories. Configure the index to apply a matching rule by associating a locale (internationalizationOID) with the attribute being indexed.• Browsing index or virtual list view (VLV) index — Improves the display performance of entries in theDirectory Server Console. A browsing index can be created on any branch in the directory tree toimprove the display performance.5.4.2. Evaluating the Costs of IndexingIndexes 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 andsubstring indexes for attributes that contain long strings, these files can grow rapidly.• Index files use memory.
