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分类: 数据库开发技术

2008-11-12 13:32:54

doc的原话,随手记录!

The SQL Access Advisor's recommendations are significantly improved if you gather structural statistics about table and index cardinalities, and the distinct cardinalities of every dimension level column, JOIN KEY column, and fact table key column. You do this by gathering either exact or estimated statistics with the DBMS_STATS package. Because gathering statistics is time-consuming and extreme statistical accuracy is not required, it is generally preferable to estimate statistics. Without these statistics, any queries referencing that table will be marked as invalid in the workload, resulting in no recommendations being made for those queries. It is also recommended that all existing indexes and materialized views have been analyzed. See Oracle Database PL/SQL Packages and Types Reference for more information regarding the DBMS_STATS package.

[@more@]http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/advisor.htm#i1026391
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