Sybase recommends that, before using the tools discussed in this chapter, you read the Performance and Tuning Series: Basics. It will help you understand the material in this chapter.
Use the optimization techniques with caution, as they allow you to override the decisions made by the Adaptive Server query processor and if misused, can have an extremely negative effect on performance. You should understand the impact on the performance of both your individual query and the possible implications for overall system performance.
In most situations, Adaptive Server advanced, cost-based query processor produces excellent query plans. However, there are times when the query processor does not choose the proper index for optimal performance, or chooses a suboptimal join order, and you must control the access methods for the query. The optimization techniques allow you to take 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 the optimization 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 query processor makes the choices that it does.
This chapter suggests workarounds for certain optimization
problems. If the workarounds do not adequately address these problems,
call Sybase Technical Support.
