【原】硬解析和物理读取vs软解析和逻辑读取

作者：david_zhang@sh 【转载时请以超链接形式标明文章】

链接：http://www.cnblogs.com/david-zhang-index/archive/2013/01/18/2866202.html

1.清空共享池和缓冲区缓存

SQL> alter system set events 'immediate trace name flush_cache';



System altered.



SQL> alter system flush shared_pool;



System altered.



SQL> set autotrace traceonly statistics

SQL> select * from dept;





Statistics

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

        355  recursive calls

          0  db block gets

         68  consistent gets

         20  physical reads

          0  redo size

        666  bytes sent via SQL*Net to client

        415  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          6  sorts (memory)

          0  sorts (disk)

          4  rows processed

2.仅清空缓冲区缓存

SQL> alter system set events 'immediate trace name flush_cache';



System altered.



SQL> set autotrace traceonly statistics

SQL> select * from dept;





Statistics

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

          0  recursive calls

          0  db block gets

          8  consistent gets

          6  physical reads

          0  redo size

        666  bytes sent via SQL*Net to client

        415  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          4  rows processed

3.都不清空

SQL> select * from dept;





Statistics

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

          0  recursive calls

          0  db block gets

          8  consistent gets

          0  physical reads

          0  redo size

        666  bytes sent via SQL*Net to client

        415  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          4  rows processed