SYS@ENMOEDU> alter system flush buffer_cache;
System altered.

清空共享池的缓存

SYS@ENMOEDU> alter system flush shared_pool;
System altered.

打开统计信息

SYS@ENMOEDU> set autotrace traceonly statistics;

执行查询语句

SYS@ENMOEDU> select * from hr.employees where department_id=60;
Statistics
----------------------------------------------------------
        197 recursive calls
          0 db block gets
        225 consistent gets
         27 physical reads
          0 redo size
       1447 bytes sent via SQL*Net to client
        420 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          6 sorts (memory)
          0 sorts (disk)
          5 rows processed

关闭统计信息

SYS@ENMOEDU> set autotrace off;

清空buffer _cache 的数据影响
SYS@ENMOEDU> alter system flush buffer_cache;

System altered.

SYS@ENMOEDU> set autotrace traceonly statistics
SYS@ENMOEDU> select * from hr.employees where department_id=60;

Statistics
----------------------------------------------------------
          0 recursive calls
          0 db block gets
          4 consistent gets
         16 physical reads
          0 redo size
       1447 bytes sent via SQL*Net to client
        420 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          5 rows processed

SYS@ENMOEDU> select * from hr.employees where department_id=60;

Statistics
----------------------------------------------------------
          0 recursive calls
          0 db block gets
          4 consistent gets
          0 physical reads
          0 redo size
       1447 bytes sent via SQL*Net to client
        420 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          5 rows processed

从上面的统计信息中看到，软解析的执行任务所耗占的资源最少

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