Database Reference
In-Depth Information
Chapter
13
DBMS-Specific Indexing
Options
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Index row suppression and exceptional conditions
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Additional index columns after the index key
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Constraints to enforce uniqueness
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Reading indexes in both directions
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Index key truncation
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Function-based indexes
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Index skip scan
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Block indexes
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Data-partitioned secondary indexes
INTRODUCTION
The number of indexing options is steadily increasing over time; this chapter
covers the more important options for traditional indexes. In addition, there is
an increasing number of application-specific index structures, such as those for
geographic databases.
The indexing options available for several DBMS products were discussed
in the previous chapter.
INDEX ROW SUPPRESSION
In nonrelational DBMSs index row suppression was a common, and commonly
used, option. The creation of an index segment or an index record could be
avoided if the indexed field had a given value, typically, blank or 0; furthermore,
exit programs could be written that would make more complex decisions. Perhaps
the pressure to reduce the size of indexes is less today because this feature is not
implemented in many relational products.
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