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OMNIDEX Indexing |
Indexing Options |
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Bitmap IndexesBitmap indexing is an indexing option which stores index pointers as a bitmap rather than a B-tree, providing efficient indexing for "low cardinality" data (small numbers of unique values). Bitmap indexes are used on low cardinality data of less than 30 unique values with well behaved Omnidex IDs. Ideal for Data Warehouse applications that do not need real time indexing. The following example shows a table with "well-behaved" IDs. One bit is assigned to each ID in the table. The bitmap index is installed on the state field.
Well-Behaved IDsA bitmap index will be created for each unique value in the column installed with the ;BM option, and each bitmap index will contain a bit for each row in the table. Therefore, the table must have a well-behaved rowid to efficiently utilize bitmap indexing. A well-behaved id must:
Databases with well-behaved rowids
Databases with ill-behaved rowids
Well-Behaved vs Ill-Behaved IDsThe following comparison demonstrates bitmap indexing for well-behaved ids versus ill-behaved ids. The first example is "well-behaved" because the ids are sequentially ascending from one.
Ill-BehavedThe next example is "ill-behaved" because the maximum value of the IDs (3,000,000) greatly exceeds the row count of the table. A bitmap index will create a bit for every possible value between 1 and the maximum value of the IDs in the table. In this example, there are 3,000,000 bits in the index for 3 records.
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Indexing Options | Indexing Strategies | Index Maintenance | Optimization | DBINSTAL |
ASK Indexes |
MDK Indexes |
Composite Indexes |
Bitmap Indexes |
Excluded Words |
Translation Table |
Special Characters |
Domains |
Omnidex IDs by Domain |
Sorted Multi-Find |
Installing the Indexes |
Building the Indexes |
Updating the Indexes |
ODXAIM |
The Explain Plan |
Nested Queries |