你看你的top sql里全是動(dòng)態(tài)采樣的sql，默認(rèn)10g以后optimizer_dynamic_sampling參數(shù)為level 2，一般為缺失統(tǒng)計(jì)信息會(huì)造成每次使用動(dòng)態(tài)采樣，雖然動(dòng)態(tài)采樣會(huì)在表頻繁發(fā)生大批量改變時(shí)，一般可以生成更好的執(zhí)行計(jì)劃，但是也不往往是這樣，所以看看 “ASSP2”."ASSP_CLOB_VOUCHER_STAMP_2020"表為什么相關(guān)SQL都走動(dòng)態(tài)采樣？

下面為該參數(shù)級別解釋Mos(Doc ID 336267.1)：

The parameter OPTIMIZER_DYNAMIC_SAMPLING controls the level of sampling performed by the optimizer.

In simplified form, the Levels have the following effects:

Level 0: Disables dynamic sampling.

Level 1: Sample all tables that have not been analyzed that meet certain criteria.

Level 2: Apply dynamic sampling to all unanalyzed tables. (Default from 10g)

Level 3: As per Level 2, plus all tables for which standard selectivity estimates used a guess for some predicate that is a potential dynamic sampling predicate.

Level 4: As per Level 3, plus all tables that have complex predicate expressions (for example single-table predicates that reference 2 or more columns or non-equality where clause predicates on two correlated columns).

Level 5-9: As per Level 4 with a larger sample size each time.

Level 10: Use dynamic sampling for all statements sampling All blocks

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