【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