Being familiar with the information presented in the Basics volume helps to understand the material in this chapter. Use caution, as the tools allow you to override the decisions made by Adaptive Server’s optimizer and can have an extreme negative effect on performance if misused. You should understand the impact on the performance of both your individual query and the possible implications for overall system performance.
Adaptive Server’s advanced, cost-based optimizer produces excellent query plans in most situations. But there are times when the optimizer does not choose the proper index for optimal performance or chooses a suboptimal join order, and you need to control the access methods for the query. The options described in this chapter allow you that control.
In addition, while you are tuning, you may want to see the effects of a different join order, I/O size, or cache strategy. Some of these options let you specify query processing or access strategy without costly reconfiguration.
Adaptive Server provides tools and query clauses that affect query optimization and advanced query analysis tools that let you understand why the optimizer makes the choices that it does.
This chapter suggests workarounds for certain optimization problems. If you experience these types of problems, please call Sybase Technical Support.