Real-time Statistics是Oracle Database 19c种针对Statistics的一个增强,也是本节主要介绍的内容。 从Oracle Database 10g开始,当我们create或rebuild index的时候,就会自动收集索引相关的统计信息,在12cR1中增加了Online Statistics Gathering for Bulk-Load,典型的比如CTAS和IIS using Direct-Path Inserts这种类型的操作(...
For example, dynamic statistics will kick in for situations where the optimizer previously would have used a guess, such as queries with LIKE predicates and wildcards. 12 W HITE PAPER / The Optimizer in Oracle Database 19c The default dynamic sampling level is 2, so it's likely that when...
21 W HITE PAPER / Understanding Optimizer Statistics with Oracle Database 19c Figure 17: Execution plan for complex predicates with dynamic sampling level 6 Dynamic sampling is controlled by the parameter OPTIMIZER_DYNAMIC_SAMPLING, which can be set to different levels (0-11). These levels ...
Hint Reporting in Oracle Database 19c Nigel Bayliss1 minute read Locked Optimizer Statistics – A Useful Tool in Your Toolbox Nigel Bayliss2 minute read Dynamic sampling and its impact on the Optimizer Nigel Bayliss7 minute read Statistics Feedback (Formerly Cardinality Feedback) ...
- dynamic statistics used: dynamic sampling (level=2) In this second example, I provided two hints on how to access the employees table. One hint requested that the primary key index be used, and the other requested that the access leverage parallel execution. ...
Adaptive dynamic sampling See"Adaptive Statistics". OPTIMIZER_MODE Sets the optimizer mode at database instance startup. Possible values areALL_ROWS,FIRST_ROWS_n, andFIRST_ROWS. OPTIMIZER_INDEX_CACHING Controls the cost analysis of an index probe with a nested loop. The range of values0to100ind...
A cyclist wants to know the most efficient bicycle route from point A to point B. A query is like the directive "I need the most efficient route from point A to point B" or "I need the most efficient route from point A to point B by way of point C." The trip advisor uses an ...
Note---dynamic sampling usedforthis statement (level=2) _optimizer_null_aware_antijoin参数能优化查询效率,但是查看mos,开启该隐含参数会有很多的bug。可能存在不稳定,因此通常会建议把该参数关闭。altersystemset"_optimizer_null_aware_antijoin"=false; 该参数...