|Oracle9i Application Developer's Guide - Large Objects (LOBs)
Release 1 (9.0.1)
Part Number A88879-01
Introduction to LOBs, 7 of 12
Oracle provides an extensible server which provides 'extensible indexing'. This allows you to define new index types as required. This is based on the concept of cooperative indexing where a data cartridge and Oracle9i build and maintain indexes for data types such as text and spatial for exampl, for On-line-Analytical Processing (OLAP).
The cartridge is responsible for defining the index structure, maintaining the index content during load and update operations, and searching the index during query processing. The index structure can be stored in Oracle as heap-organized, or an index-organized table, or externally as an operating system file.
To this end, Oracle introduces the concept of an indextype. The purpose of an indextype is to enable efficient search and retrieval functions for complex domains such as text, spatial, image, and OLAP by means of a data cartridge. An indextype is analogous to the sorted or bit-mapped index types that are built-in within the Oracle Server. The difference is that an indextype is implemented by the data cartridge developer, whereas the Oracle kernel implements built-in indexes. Once a new indextype has been implemented by a data cartridge developer, end users of the data cartridge can use it just as they would built-in indextypes.
When the database system handles the physical storage of domain indexes, data cartridges
By supporting extensible indexes, Oracle9i significantly reduces the effort needed to develop high-performance solutions that access complex datatypes such as LOBs.
The extensible optimizer functionality allows authors of user-defined functions and indexes to create statistics collection, selectivity, and cost functions. This information is used by the optimizer in choosing a query plan. The cost-based optimizer is thus extended to use the user-supplied information; the rule-based optimizer is unchanged.
Extensible indexing functionality allows you to define new operators, index types, and domain indexes. For such user-defined operators and domain indexes, the extensible optimizer functionality will allow users to control the three main components used by the optimizer to select an execution plan: statistics, selectivity, and cost.