TECHNIQUE FOR FACTORING UNCERTAINTY INTO COST-BASED QUERY OPTIMIZATION

摘要

A technique for factoring uncertainty into cost-based query optimization includes: determining the degree of uncertainty involved in the cost estimates for the query, determining the degree of sensitivity the query has to that uncertainty, and determining if there is an access path that performs well across the range of possible conditions that could occur at execution time, reducing the risk of performance spikes and performance volatility. If such an access path exists, select that access path; if not, perform parametric query optimization or query re-optimization.

主权项

1. A method of generating an optimal access path to data for a query being performed by a computer system to retrieve data from a database stored in a data storage device coupled to the computer system, the method comprising:
generating a plurality of access paths for the query; determining an uncertainty for the query, wherein the uncertainty is the difference between selectivity assumptions about the costs for each of the access paths; determining a sensitivity of the query to the uncertainty, wherein the sensitivity is the difference between the costs of the access paths for the selectivity assumptions; and selecting one of the access paths according to the uncertainty and the sensitivity.