在Oracle9i中，即使一个完全相同的过程的重建，Oracle也需要重新编译过程，这个可以从LAST_DDL_TIME看出：

    [oracle@jumper oracle]$ sqlplus eygle/eygle

    SQL*Plus: Release 9.2.0.4.0 - Production on Sat Mar 31 17:52:55 2007

    Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

    Connected to:

    Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production

    With the Partitioning option

    JServer Release 9.2.0.4.0 - Production

    SQL> create or replace PROCEDURE pining

    2 IS

    3 BEGIN

    4 NULL;

    5 END;

    6 /

    Procedure created.

    SQL> select object_name,last_ddl_time from dba_objects where object_name='PINING';

    OBJECT_NAME LAST_DDL_TIME

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

    PINING 2007-03-31 17:52:58

    SQL> create or replace PROCEDURE pining

    2 IS

    3 BEGIN

    4 NULL;

    5 END;

    6 /

    Procedure created.

    SQL> select object_name,last_ddl_time from dba_objects where object_name='PINING';

    OBJECT_NAME LAST_DDL_TIME

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

    PINING 2007-03-31 17:54:35

    在Oracle10g中，这个LAST_DDL_TIME不再变化，这说明在10g中，当我们执行create or replace PROCEDURE 时，Oracle现在先尝试进行过程检查，如果内容没有变化，则不需要对过程进行重新编译，这可以减少Cache中的Invalidation，从而可以减少竞争：

    $ sqlplus eygle/eygle

    SQL*Plus: Release 10.2.0.1.0 - Production on Sat Mar 31 17:44:46 2007

    Copyright (c) 1982, 2005, Oracle. All rights reserved.

    Connected to:

    Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - 64bit Production

    With the Partitioning, OLAP and Data Mining options

    SQL> create or replace PROCEDURE pining

    2 IS

    3 BEGIN

    4 NULL;

    5 END;

    6 /

    Procedure created.

    SQL> alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';

    Session altered.

    SQL> col object_name for a30

    SQL> select object_name,last_ddl_time from dba_objects where object_name='PINING';

    OBJECT_NAME LAST_DDL_TIME

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

    PINING 2007-03-31 17:45:25

    SQL> create or replace PROCEDURE pining

    2 IS

    3 BEGIN

    4 NULL;

    5 END;

    6 /

    Procedure created.

    SQL> select object_name,last_ddl_time from dba_objects where object_name='PINING';

    OBJECT_NAME LAST_DDL_TIME

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

    PINING 2007-03-31 17:45:25

    然而这个变化是否有效呢？请看我接下来的另外一个测试...

    -to be continued ....

    -----