Oradebug 推进scn

环境：LINUX_x86

这里需要注意地方为:

1.我的系统为32bit的小端系统.
2.大小端的SCN_WRAP和SCN_BASE是相反的.在大端中,kcsgscn_的前4字节为SCN_BASE,5-8字节为SCN_WRAP.
3.在32bit系统中寻址只能是4字节,而64位系统可以8字节.

该测试为32bit 小端系统,环境如下:

[root@ludatou ~]# file /sbin/init
/sbin/init: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped

[root@ludatou ~]# su - ora10g
[ora10g@ludatou ~]$ sqlplus '/as sysdba'

SQL*Plus: Release 10.2.0.4.0 - Production on Thu Jul 24 01:58:10 2014

Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> startup mount
ORACLE instance started.

Total System Global Area  318767104 bytes
Fixed Size                  1267260 bytes
Variable Size             100665796 bytes
Database Buffers          213909504 bytes
Redo Buffers                2924544 bytes
Database mounted.

检查当前scn情况并以oradebug的方式推进scn:

--当前scn
SQL> select to_char(checkpoint_change#,'XXXXXXXXXXXXXXXX') from v$database;

TO_CHAR(CHECKPOIN
-----------------
A03E2F

SQL> oradebug setmypid
Statement processed.

--获取内存scn对应
SQL> oradebug dumpvar sga kcsgscn_
kcslf kcsgscn_ [20009228, 20009248) = 00000000 00000000 00000000 00000000 00000000 00000000 00000000 20009034
--因为32bit系统所以采用4字节寻址,更改scn_wrap
SQL> oradebug poke 0x20009228 4 0x01
BEFORE: [20009228, 2000922C) = 00000000
AFTER: [20009228, 2000922C) = 00000001
--更改scn_base
SQL> oradebug poke 0x2000922C 4 0x01
BEFORE: [2000922C, 20009230) = 00000000
AFTER: [2000922C, 20009230) = 00000001
SQL> oradebug dumpvar sga kcsgscn_
kcslf kcsgscn_ [20009228, 20009248) = 00000001 00000001 00000000 00000000 00000000 00000000 00000000 20009034
SQL> oradebug poke 0x2000922C 4 0xA03E2F
BEFORE: [2000922C, 20009230) = 00000001
AFTER: [2000922C, 20009230) = 00A03E2F
SQL> oradebug dumpvar sga kcsgscn_
kcslf kcsgscn_ [20009228, 20009248) = 00000001 00A03E2F 00000000 00000000 00000000 00000000 00000000 20009034
--更改完成后打开数据
SQL> alter database open;

Database altered.
--可以发现scn已经推进了wrap+1位
SQL> select to_char(current_scn,'XXXXXXXXXXXXXXXX') from v$database;

TO_CHAR(CURRENT_S
-----------------
100A04185