在Oracle9i中，即使一個完全相同的過程的重建，Oracle也需要重新編譯過程，這個可以從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，這個LAST_DDL_TIME不再變化，這說明在10g中，當我們執行create or replace PROCEDURE 時，Oracle現在先嘗試進行過程檢查，假如內容沒有變化，則不需要對過程進行重新編譯，這可以減少Cache中的Invalidation， 從而可以減少競爭：
$ 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
然而這個變化是否有效呢？請看我接下來的另外一個測試... -to be continued .... -----
