XML schema for plan optimization guidelines
Plan optimization guidelines can consist of access requests or join requests.
- An access request specifies an access method for a table reference.
- A join request specifies a method and sequence for performing a join operation. Join requests are composed of other access or join requests.
Most of the available access requests correspond to the optimizer's data access methods, such as table scan, index scan, and list prefetch, for example. Most of the available join requests correspond to the optimizer's join methods, such as nested-loop join, hash join, and merge join. Each access request or join request element can be used to influence plan optimization.