|Oracle 8i Data Cartridge Developer's Guide
Release 2 (8.1.6)
Part Number A76937-01
Query Optimization, 7 of 7
A statistics type is defined as a regular object type. Since object types must have at least one attribute, a statistics type also must have at least one attribute. This will be a dummy attribute, however, since it will never be set or accessed.
In Oracle8i domain indexes are non-partitioned and serial. The optimizer computes the composite cost of a domain index access path assuming a serial execution.
Oracle's distributed implementation does not support adding functions to the remote capabilities list. All functions referencing remote tables are executed as filters. The placement of the filters occurs outside the optimizer. The cost model reflects this implementation and does not attempt to optimize placement of these predicates.
Since predicates are not shipped to the remote site, you cannot use domain indexes on remote tables. Therefore, the
DESCRIBE protocol is unchanged, and remote domain indexes are not visible from the local site.
The cost of execution of the queries remains the same with the extensible optimizer if the same plan is chosen. If a different plan is chosen, the execution time should be better assuming that the user-defined cost, selectivity, and statistics collection functions are accurate. In light of this, you are strongly encouraged to provide statistics collection, selectivity, and cost functions for user-defined structures because the optimizer defaults can be inaccurate and lead to an expensive execution plan.