# 2일차

show parameter sort\_area\_size;

show parameter hash\_area\_size;

alter session set sort\_area\_size = 1097152;

select \* from v$object\_usage;

alter index PK\_EMP MONITORING USAGE;

모든 sql이 인덱스를 사용해야만 하는가?

* 10\~15 % 이하의 데이터를 처리하는 경우에 효율적, 그이상은 인덱스를 사용하지 않는 것이 더 좋다. 

인덱스

* B tree
  * 주기적인 리빌딩 필요.

```sql
select MAX(SEQ) + 1
from product
where dept = '12300';
```

멀티 블록 읽기

* DB\_FILE\_MULTIBLOCKREAD\_COUNT = 4 -> 8개로 늘리는 것도 튜닝포인

```sql
INSERT /*+ PARALLEL(A,4) */
INTO EX_EXAM_QAPPLY_2 A
SELECT /*+ PARALLEL(B,4) */
*
FROM EX_EXAM_QAPPLY B;
```

인덱스를 타지 않는 경우 

* 부정연산자
* null 값


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