理解 alter system flush buffer_cache;_顺风耳

http://blog.sina.com.cn/u/1404401102

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正文字体大小：大中小

理解 alter system flush buffer_cache;

(2014-05-25 00:11:24)

标签：

it

分类： SAP_Basis

理解 alter system flush buffer_cache;

SQL> set timing on

SQL> set autot trace statistic;

SQL> select count(*) from emp;

Elapsed: 00:00:00.04

Statistics

----------------------------------------------------------

4 recursive calls

0 db block gets

13 consistent gets

8 physical reads

0 redo size

526 bytes sent via SQL*Net to client

524 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

1 rows processed

SQL> select count(*) from emp;

Elapsed: 00:00:00.01

Statistics

----------------------------------------------------------

0 recursive calls

0 db block gets

4 consistent gets

0 physical reads

0 redo size

526 bytes sent via SQL*Net to client

524 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

1 rows processed

SQL> alter system flush buffer_cache;

System altered.

Elapsed: 00:00:00.07

SQL> select count(*) from emp;

Elapsed: 00:00:00.04

Statistics

----------------------------------------------------------

4 recursive calls

0 db block gets

13 consistent gets

8 physical reads

0 redo size

526 bytes sent via SQL*Net to client

524 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

1 rows processed

更多可参考：http://blog.itpub.net/519536/viewspace-623381

提醒：

(1)当Buffer Cache包含大量数据时，刷新时间将会很长，没有“特殊需求”请不要使用这个方法，不建议在生产环境这样干！

(2)该方法在进行SQL性能测试时较为常用，为排除Buffer Cache对于测试结果影响时可以考虑使用该方法强制Oracle重新执行物理读。

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