alter database character set INTERNAL_CONVERT ZHS16GBK Updating character set in controlfile to ZHS16GBK SYS.SNAP$ (REL_QUERY) - CLOB representation altered SYS.METASTYLESHEET (STYLESHEET) - CLOB representation altered SYS.EXTERNAL_TAB$ (PARAM_CLOB) - CLOB representation altered XDB.XDB$RESOURCE (SYS_NC00027$) - CLOB representation altered ODM.ODM_PMML_DTD (DTD) - CLOB representation altered OE.WAREHOUSES (SYS_NC00003$) - CLOB representation altered PM.ONLINE_MEDIA (SYS_NC00042$) - CLOB representation altered PM.ONLINE_MEDIA (SYS_NC00062$) - CLOB representation altered PM.ONLINE_MEDIA (PRODUCT_TEXT) - CLOB representation altered PM.ONLINE_MEDIA (SYS_NC00080$) - CLOB representation altered PM.PRINT_MEDIA (AD_SOURCETEXT) - CLOB representation altered PM.PRINT_MEDIA (AD_FINALTEXT) - CLOB representation altered Completed: alter database character set INTERNAL_CONVERT ZHS1 |
在这里面,我们看到这样一条重要的,Oracle非公开的命令:
|
这个命令是当你选择了使用典型方式创建了种子数据库以后,Oracle会根据你选择的字符集设置,把当前种子数据库的字符集更改为期望字符
集,这就是这条命令的作用.
在使用这个命令时,Oracle会跳过所有子集及超集的检查,在任意字符集之间进行强制转换,所以,使用这个命令时你必须十分小心,你必须
清楚这一操作会带来的风险.
我们之前讲过的内容仍然有效,你可以使用csscan扫描整个数据库,如果在转换的字符集之间确认没有严重的数据损坏,或者你可以使用有效
的方式更改,你就可以使用这种方式进行转换.
我们来看一下具体的操作过程及Oracle的内部操作:
这是alert.log文件中的记录信息:
Tue Oct 19 16:26:30 2004
Database Characterset is ZHS16GBK
replication_dependency_tracking turned off (no async multimaster replication found)
Completed: ALTER DATABASE OPEN
Tue Oct 19 16:27:07 2004
alter database character set INTERNAL_USE ZHS16CGB231280
Updating character set in controlfile to ZHS16CGB231280
Tue Oct 19 16:27:15 2004
Thread 1 advanced to log sequence 118
Current log# 2 seq# 118 mem# 0: /opt/oracle/oradata/primary/redo02.log
Tue Oct 19 16:27:15 2004
ARC0: Evaluating archive log 3 thread 1 sequence 117
ARC0: Beginning to archive log 3 thread 1 sequence 117
Creating archive destination LOG_ARCHIVE_DEST_1: '/opt/oracle/oradata/primary/archive/1_117.dbf'
ARC0: Completed archiving log 3 thread 1 sequence 117
Tue Oct 19 16:27:20 2004
Completed: alter database character set INTERNAL_USE ZHS16CGB231280
Shutting down instance: further logons disabled
Shutting down instance (immediate)
License high water mark = 1
Tue Oct 19 16:29:06 2004
ALTER DATABASE CLOSE NORMAL
...
...
格式化10046跟踪文件,得到以下信息(摘要):
alter session set events '10046 trace name context forever,level 12' alter database character set INTERNAL_USE ZHS16CGB231280 call count cpu elapsed disk query current rows ------- ------ -------- ---------- ---------- ---------- ---------- ---------- Parse 1 0.00 0.00 0 0 0 0 Execute 1 4.88 6.04 910 16825 18099 0 Fetch 0 0.00 0.00 0 0 0 0 ------- ------ -------- ---------- ---------- ---------- ---------- ---------- total 2 4.88 6.04 910 16825 18099 0 Misses in library cache during parse: 1 Optimizer goal: CHOOSE Parsing user id: SYS Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ control file sequential read 4 0.00 0.00 control file parallel write 2 0.05 0.08 log file sync 2 0.08 0.08 SQL*Net message to client 1 0.00 0.00 SQL*Net message from client 1 18.06 18.06 ******************************************************************************** .... update col$ set charsetid = :1 where charsetform = :2 .... update argument$ set charsetid = :1 where charsetform = :2 .... update collection$ set charsetid = :1 where charsetform = :2 .... update attribute$ set charsetid = :1 where charsetform = :2 .... update parameter$ set charsetid = :1 where charsetform = :2 .... update result$ set charsetid = :1 where charsetform = :2 .... update partcol$ set spare1 = :1 where charsetform = :2 .... update subpartcol$ set spare1 = :1 where charsetform = :2 .... update props$ set value$ = :1 where name = :2 .... update "SYS"."KOTAD$" set SYS_NC_ROWINFO$ = :1 where SYS_NC_OID$ = :2 .... update seq$ set increment$=:2,minvalue=:3,maxvalue=:4,cycle#=:5,order$=:6, cache=:7,highwater=:8,audit$=:9,flags=:10 where obj#=:1 .... update kopm$ set metadata = :1, length = :2 where name='DB_FDO' .... ALTER DATABASE CLOSE NORMAL |
此处生成的日志你可以在这里下载(供参考):
http://www.eygle.com/special/primary_ora_13730.zip
http://www.eygle.com/special/primary_ora_13730.tkf.log
我们看到这个过程和之前ALTER DATABASE CHARACTER SET操作的内部过程是完全相同的,也就是说INTERNAL_USE提供的帮助就是使
Oracle数据库绕过了子集与超集的校验.
这一方法在某些方面是有用处的,比如测试;应用于产品环境大家应该格外小心,除了你以外,没有人会为此带来的后果负责:
结语(我们不妨再说一次):
对于DBA来说,有一个很重要的原则就是:不要把你的数据库置于危险的境地!
这就要求我们,在进行任何可能对数据库结构发生改变的操作之前,先做有效的备份,很多DBA没有备份的操作中得到了惨痛的教训。
本文作者:
eygle,Oracle技术关注者,来自中国最大的Oracle技术论坛itpub.
www.eygle.com是作者的个人站点.你可通过Guoqiang.Gai@gmail.com来联系作者.欢迎技术探讨交流以及链接交换.
原文出处:
http://www.eygle.com/special/NLS_CHARACTER_SET_07.htm