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，假如内容没有变化，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 .... -----