非公开HINT-终级Hint:CARDINALITY 这个hint实在是Oracle SQL tunning的终极杀手锏,用我们对数据分布的理解强制给Oracle洗脑。用在多表连接或者存在in-list & exists的时候,选择驱动表,尤其适合。 This hint specifies the estimated cardinality returned by a query or portions of the query. Note if no table is ...
115 6.1.1 all_rows和first_rows(cbo) 115 6.1.2 rule hint 117 6.2 访问路径相关的hint 117 6.2.1 full hint 118 6.2.2 index hint 118 6.2.3 no_index hint 118 6.2.4 index_desc hint 119 6.2.5 index_combine hint 119 6.2.6 index_ffs 119 6.2.7 index_join 120 6.2.8 index_ss hint ...
hint : opt_param(‘_optimizer_use_feedback’ ‘false’)修改参数： alter system set “_optimizer...
对于上述问题可选的常见方案是若有这样问题的SQL较少则考虑加HINT或者SQL PROFILE,若较多还是需要考虑减少这种谓词左边有函数的现象。 implicit data_type conversion functions in Filter Predicates. Review Execution Plans. If Filter Predicatesinclude unexpected INTERNAL_FUNCTION to perform an implicit data_type con...
There is also a possibility to add an opt_param hint at the session level to disable cardinality feedback for a specific query as follows: select /*+ opt_param('_optimizer_use_feedback' 'false') */ ... Is Statistics Feedback persistent when the cursor is aged out?
At this point, we could consider running the query again with the /*+ gather_plan_statistics */ hint in place – and in another 22 hours or so we would be able to compare estimates with actuals to see how accurate that cardinality estimate of one row really was! Since running the whol...
hint:cardinality(test, 1)强制使用 查看share pool中还有那些sql用到了feedback select sql_ID,USE_FEEDBACK_STATS FROM V$SQL_SHARED_CURSOR where USE_FEEDBACK_STATS =’Y’; CF特性的功能是非常不错的,oracle在使用了cf反馈评估后更准确的统计数据后会根据此数据生成对于的plan,在再次的执行中还会持续评估统...
hint:cardinality(test, 1)强制使用 查看share pool中还有那些sql用到了feedback select sql_ID,USE_FEEDBACK_STATS FROM V$SQL_SHARED_CURSOR where USE_FEEDBACK_STATS =’Y’; CF特性的功能是非常不错的,oracle在使用了cf反馈评估后更准确的统计数据后会根据此数据生成对于的plan,在再次的执行中还会持续评估统...
hint:cardinality(test, 1)强制使用 查看share pool中还有那些sql用到了feedback select sql_ID,USE_FEEDBACK_STATS FROM V$SQL_SHARED_CURSOR where USE_FEEDBACK_STATS =’Y’; CF特性的功能是非常不错的,oracle在使用了cf反馈评估后更准确的统计数据后会根据此数据生成对于的plan,在再次的执行中还会持续评估统...
Oracle 11gR2针对此特性,也专门在V$SQL_SHARED_CURSOR中增加了USE_FEEDBACK_STATS列来记录SQL是否使用了基数反馈。基数反馈的开启和关闭通过一个隐含参数“_OPTIMIZER_USE_FEEDBACK”来控制,该参数默认为TRUE,表示开启技术反馈特性。此参数除了可以在SESSION和SYSTEM级别进行设置之外,还可以在SQL语句级使用Hint进行开启和...