Red Hat DIRECTORY SERVER 8.0, Руководство администратора

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Chapter 10. Managing Indexes
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10.1.4. Approximate Searches
In addition, the directory uses a variation of the metaphone phonetic algorithm to perform searches
on an approximate index. Each value is treated as a sequence of words, and a phonetic code is
generated for each word.
NOTE
The metaphone phonetic algorithm in Directory Server supports only US-ASCII letters.
Therefore, use approximate indexing only with English values.
Values entered on an approximate search are similarly translated into a sequence of phonetic codes.
An entry is considered to match a query if both of the following are true:
• All of the query string codes match the codes generated in the entry string.
• All of the query string codes are in the same order as the entry string codes.
Name in the Directory
(Phonetic Code)
Query String (Phonetic code) Match Comments
Alice B Sarette (ALS B SRT) Alice Sarette (ALS SRT) Matches. Codes are specified
in the correct order.
Alice Sarrette (ALS SRT) Matches. Codes are specified
in the correct order, despite the
misspelling of Sarette.
Surette (SRT) Matches. The generated code
exists in the original name,
despite the misspelling of
Sarette.
Bertha Sarette (BR0 SRT) No match. The code BR0 does
not exist in the original name.
Sarette, Alice (SRT ALS) No match. The codes are not
specified in the correct order.
10.1.5. Balancing the Benefits of Indexing
Before creating new indexes, balance the benefits of maintaining indexes against the costs.
• Approximate indexes are not efficient for attributes commonly containing numbers, such as
telephone numbers.
• Substring indexes do not work for binary attributes.
• Equality indexes should be avoided if the value is big (such as attributes intended to contain
photographs or passwords containing encrypted data).
• Maintaining indexes for attributes not commonly used in a search increases overhead without
improving global searching performance.
• Attributes that are not indexed can still be specified in search requests, although the search
performance may be degraded significantly, depending on the type of search.