?驗證?explain?plan命令???與??set?autotrace命令??是否為真實執行計劃

??????0??CONN?/AS?SYSDBA;?????

?

??????1??create?table?t1?as?select?*?from?dba_objects;

???

??????2??insert?into?t1?select?*?from?t1;

?

??????3???commit;

?

??????4???select?count(1)?from?t1;

?

??????5???create?index?idx_t1?on?t1(object_id);

????????--收集統計信息

??????6???exec?dbms_stats.gather_table_stats(ownname=>'SYS',tabname=>'T1',estimate_percent=>?100,cascade=>?true);

??????

??????7???select?*?from?table(dbms_xplan.display);

?

??????

?

?????

??????8?

????

VAR?X?NUMBER;

VAR?Y?NUMBER;

EXEC?:X?:=0;

EXEC:Y?:=100000;

?

????????--explain命令

????????EXPLAIN??PLAN?FOR?SELECT?count(*)?from?t1?where?object_id?between?:x?and?:y;

?

????????select?*?from?table(dbms_xplan.display);

?

???????

?

??????????顯示走idx_t1索引范圍（range）掃描

?

????????select?count(*)?from?t1?where?object_id?between?:x?and?:y;

?

????????--dbms_xplan.display_cursor(null,null,'ADVANCED')??得到真實執行計劃

????????select?*?from?table(dbms_xplan.display_cursor(null,null,'ADVANCED'));

?

?

?

?

?

????????

Index?fast?full??快速全掃描

?

?

---set?autotrace?traceonly?驗證

?

Set?autotrace?traceonly

Select?count(*)?from?t1?where?object_id?between?:x?and?:y;

?

?顯示走idx_t1索引范圍（range）掃描

?

結論:使用set?autotrace,set?autotrace?源于explain?plan是不準確的,特別是綁定變量下查詢是不準確的

-dbms_xplan.display_cursor(null,null,'ADVANCED')?

和10046事件獲取真實的執行計劃

轉載于:https://www.cnblogs.com/kool/p/6695597.html

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