使用BBED修改SCN
Posted on May 9, 2012 at 5:30 pm by vogts
文章来源：http://www.alidba.net/index.php/archives/594
下面这个错误，我想是很多DBA的痛。
@>startup ;
ORACLE instance started.
Total System Global Area 838860800 bytes
Fixed Size 2087608 bytes
Variable Size 494929224 bytes
Database Buffers 335544320 bytes
Redo Buffers 6299648 bytes
Database mounted.
ORA-01113: file 5 needs media recovery
ORA-01110: data file 5: ‘/data/oracle/oradata/orcl/wt_tbs01.dbf’
有备份还好，没备份基本上只有把数据文件offline了。DBA准备打包回家吧。
经过无数次的测试，确认修改SCN号可以搞定。目前网上的文章，多少还是有些错误。经过反复的测试，确认没有问题。
我们直接使用BBED查看下当前SYSTEM TBS表空间的SCN号：
BBED> set file 1
FILE# 1
数据文件头就是第一个block块，因此我们不需要设置其他block块，
此外map可以显示block里的详细信息。我们发现就一个“kcvfh”，OK直接查看这个吧。
BBED> map
File: /data/oracle/oradata/bops10g/system01.dbf (1)
Block: 1 Dba:0×00400001
————————————————————
Data File Header
struct kcvfh, 676 bytes @0
ub4 tailchk @8188
print出来的内容太多，我做了删剪，留下我们有用的内容。
BBED> print kcvfh
struct kcvfh, 676 bytes @0
…………………………
struct kcvfhckp, 36 bytes @484
struct kcvcpscn, 8 bytes @484
ub4 kscnbas @484 0×000748bf–SCN的低位
ub2 kscnwrp @488 0×0000–SCN的高位
ub4 kcvcptim @492 0×2ea86f92 –最后一次checkpoint time
ub2 kcvcpthr @496 0×0001
………………………………
ub4 kcvfhcpc @140 0×0000007f—checkpoint count
ub4 kcvfhrts @144 0×2ea86844
ub4 kcvfhccc @148 0×0000007e
–oracle 一个TBS最多30个字符，通过BBED ，我们发现这里是定长的
text kcvfhtnm[0] @338 S
text kcvfhtnm[1] @339 Y
text kcvfhtnm[2] @340 S
text kcvfhtnm[3] @341 T
text kcvfhtnm[4] @342 E
text kcvfhtnm[5] @343 M
text kcvfhtnm[6] @344
text kcvfhtnm[7] @345
text kcvfhtnm[8] @346
text kcvfhtnm[9] @347
text kcvfhtnm[10] @348
text kcvfhtnm[11] @349
text kcvfhtnm[12] @350
text kcvfhtnm[13] @351
text kcvfhtnm[14] @352
text kcvfhtnm[15] @353
text kcvfhtnm[16] @354
text kcvfhtnm[17] @355
text kcvfhtnm[18] @356
text kcvfhtnm[19] @357
text kcvfhtnm[20] @358
text kcvfhtnm[21] @359
text kcvfhtnm[22] @360
text kcvfhtnm[23] @361
text kcvfhtnm[24] @362
text kcvfhtnm[25] @363
text kcvfhtnm[26] @364
text kcvfhtnm[27] @365
text kcvfhtnm[28] @366
text kcvfhtnm[29] @367
………………………………
这4个offset的位置内容，文档上是这样说的：
Oracleconsiders four attributes of this data structure when determining if a datafile is sync with the other data files of the database:
（1）kscnbas (at offset 484) - SCN of last change to the datafile.
（2）kcvcptim (at offset 492) -Time of the last change to the datafile.
（3）kcvfhcpc (at offset 140) - Checkpoint count.
（4）kcvfhccc (at offset 148) - Unknown, but is always 1 less than thecheckpoint point count.
oracle主要通过这4个来判断一致性，至于中文说明，我也写在上面了。
接下去，我们看看坏掉的wt-tbs01.dbf的信息：
wt_tbs.dbf
struct kcvfhckp, 36 bytes @484
struct kcvcpscn, 8 bytes @484
ub4 kscnbas @484 0×000747a5
ub2 kscnwrp @488 0×0000
ub4 kcvcptim @492 0×2ea86f03
ub2 kcvcpthr @496 0×0001
union u, 12 bytes @500
struct kcvcprba, 12 bytes @500
ub4 kcrbaseq @500 0×00000004
ub4 kcrbabno @504 0×00000019
ub2 kcrbabof @508 0×0010
**********************
ub4 kcvfhcpc @140 0×00000007
ub4 kcvfhrts @144 0×2ea86844
ub4 kcvfhccc @148 0×00000006
好，484，492，140，148直接修改就好了。
/**************
484
****************/
ub4 kscnbas @484 0×000747a5-> 0×000748bf–> bf487400
set offset 484
modify /x bf48
set offset 486
modify /x 0700
/**************
492
******************/
ub4 kcvcptim @492 0×2ea86f03->0×2ea86f92 –>926fa8ea
set offset 492
modify /x 926f
set offset 494
modify /x a82e
/**************
140
******************/
ub4 kcvfhcpc @140 0×00000007->0×0000007f–>7f000000
set offset 140
modify /x 7f00
set offset 142
modify /x 0000
/**************
148
**************/
ub4 kcvfhccc @148 0×00000006->0×0000007e->7e000000
set offset 148
modify /x 7e00
set offset 150
modify /x 0000
最后做下checksum，就OK了
BBED> sum dba 5,1 apply
Check value for File 5, Block 1:
current = 0×554c, required = 0×554c
接下去就简单了，重建控制文件，数据库OPEN RESETLOG搞定
@>startup nomount;
ORACLE instance started.
Total System Global Area 838860800 bytes
Fixed Size 2087608 bytes
Variable Size 494929224 bytes
Database Buffers 335544320 bytes
Redo Buffers 6299648 bytes
@>CREATE CONTROLFILE REUSE DATABASE “orcl” RESETLOGS NOARCHIVELOG
2 MAXLOGFILES 5
3 MAXLOGMEMBERS 5
4 MAXDATAFILES 100
5 MAXINSTANCES 1
MAXLOGHISTORY 292
6 7 LOGFILE
8 GROUP 1 ‘/data/oracle/oradata/orcl/redo101.log’ SIZE 10M,
9 GROUP 2 ‘/data/oracle/oradata/orcl/redo201.log’ SIZE 10M,
10 GROUP 3 ‘/data/oracle/oradata/orcl/redo301.log’ SIZE 10M
11 — STANDBY LOGFILE
12 DATAFILE
13 ‘/data/oracle/oradata/orcl/system01.dbf’,
14 ‘/data/oracle/oradata/orcl/undotbs01.dbf’,
15 ‘/data/oracle/oradata/orcl/sysaux01.dbf’,
16 ‘/data/oracle/oradata/orcl/users01.dbf’,
17 ‘/data/oracle/oradata/orcl/wt_tbs01.dbf’
18 CHARACTER SET US7ASCII
19 ;
Control file created.
@>RECOVER DATABASE USING BACKUP CONTROLFILE
ORA-00279: change 477375 generated at 05/09/2012 01:49:06 needed for thread 1
ORA-00289: suggestion : /data/oracle/arch/orcl/1_4_782784012.arc
ORA-00280: change 477375 for thread 1 is in sequence #4
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
Media recovery cancelled.
@>ALTER DATABASE OPEN RESETLOGS;
Database altered.
总结一下:
其实本人不懂其中的原理,可能功力不够,用了一个原始的方法,分别2个块的print kcvfh内容导入文件比较,修改其中四个值
（1）kscnbas (at offset 484) - SCN of last change to the datafile.
（2）kcvcptim (at offset 492) -Time of the last change to the datafile.
（3）kcvfhcpc (at offset 140) - Checkpoint count.
（4）kcvfhccc (at offset 148) - Unknown, but is always 1 less than thecheckpoint point count.
与正确的文件一致!
备份控制文件:
alter database backup controlfile to 'd:\20080326.ctl';(备份成二进制文件)
alter database backup controlfile to trace;(备份创建控制文件的脚本，在udump目录下)
记录一下,说不定用得上
bbed修改scn
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转载自aigo-h.iteye.com/blog/1933390
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