记一次数据库参数compatible降级
众所周知，Oracle参数compatible 主要用于启用Oracle针对某一版本的新特性。但此参数设置时，只能往上调，设置好之后不能往下降。
System altered.
重启数据库后alert日志会有如下显示，从alert日志中可以明显的看出，compatible升级之后，Oracle会修改控制文件和redolog
MAXLOGFILES 5
MAXLOGMEMBERS 5
MAXDATAFILES 100
MAXINSTANCES 1
MAXLOGHISTORY 292
LOGFILE
GROUP 1 '/oradata/mynewdb/redo01.log' SIZE 100M,
GROUP 2 '/oradata/mynewdb/redo02.log' SIZE 100M,
GROUP 3 '/oradata/mynewdb/redo03.log' SIZE 100M
-- STANDBY LOGFILE
DATAFILE
'/oradata/mynewdb/system01.dbf',
'/oradata/mynewdb/undotbs01.dbf',
'/oradata/mynewdb/sysaux01.dbf'
CHARACTER SET ZHS16GBK
;
--ORACLE instance started.
Total System Global Area 524288000 bytes
Fixed Size 1262716 bytes
Variable Size 167775108 bytes
Database Buffers 348127232 bytes
Redo Buffers 7122944 bytes
SQL> CREATE CONTROLFILE REUSE DATABASE "MYNEWDB" RESETLOGS NOARCHIVELOG
*
ERROR at line 1:
ORA-01503: CREATE CONTROLFILE failed
ORA-01130: database file version 10.2.0.2.0 incompatible with ORACLE version
10.2.0.1.0
ORA-01110: data file 1: '/oradata/mynewdb/system01.dbf'
至此，我们只能通过修改数据文件头的compatible来达到降级的目的了
MAXLOGFILES 5
MAXLOGMEMBERS 5
MAXDATAFILES 100
MAXINSTANCES 1
MAXLOGHISTORY 292
LOGFILE
GROUP 1 '/oradata/mynewdb/redo01.log' SIZE 100M,
GROUP 2 '/oradata/mynewdb/redo02.log' SIZE 100M,
GROUP 3 '/oradata/mynewdb/redo03.log' SIZE 100M
-- STANDBY LOGFILE
DATAFILE
'/oradata/mynewdb/system01.dbf',
'/oradata/mynewdb/undotbs01.dbf',
'/oradata/mynewdb/sysaux01.dbf'
CHARACTER SET ZHS16GBK
;ORACLE instance started.
Total System Global Area 524288000 bytes
Fixed Size 1262716 bytes
Variable Size 176163716 bytes
Database Buffers 339738624 bytes
Redo Buffers 7122944 bytes
SQL> CREATE CONTROLFILE REUSE DATABASE "MYNEWDB" NORESETLOGS NOARCHIVELOG
*
ERROR at line 1:
ORA-01503: CREATE CONTROLFILE failed
ORA-00331: log version 0.0.0.0.0 incompatible with ORACLE version 10.2.0.1.0
ORA-01517: log member: '/oradata/mynewdb/redo01.log'
于是我们采用reselogs选项重建控制文件，终于成功
2 MAXLOGFILES 5
3 MAXLOGMEMBERS 5
4 MAXDATAFILES 100
5 MAXINSTANCES 1
6 MAXLOGHISTORY 292
7 LOGFILE
8 GROUP 1 '/oradata/mynewdb/redo01.log' SIZE 100M,
9 GROUP 2 '/oradata/mynewdb/redo02.log' SIZE 100M,
10 GROUP 3 '/oradata/mynewdb/redo03.log' SIZE 100M
11 -- STANDBY LOGFILE
12 DATAFILE
13 '/oradata/mynewdb/system01.dbf',
14 '/oradata/mynewdb/undotbs01.dbf',
15 '/oradata/mynewdb/sysaux01.dbf'
16 CHARACTER SET ZHS16GBK
17 ;
Control file created.
重建好控制文件后，在open resetlogs时提示需要recover，redolog文件头的版本号依然为10.2.0.2.0，于是recover出现了问题
引用SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01113: file 1 needs media recovery
ORA-01110: data file 1: '/oradata/mynewdb/system01.dbf'
SQL> recover database using backup controlfile;
ORA-00279: change 823455 generated at 05/13/2011 12:05:45 needed for thread 1
ORA-00289: suggestion :
/ora10g/oracle/product/10.2.0/db_1/dbs/arch1_11_748203362.dbf
ORA-00280: change 823455 for thread 1 is in sequence #11
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
/oradata/mynewdb/redo01.log
ORA-00331: log version 10.2.0.2.0 incompatible with ORACLE version 10.2.0.1.0
ORA-00334: archived log: '/oradata/mynewdb/redo01.log'
出现这个错误之后，其实修复也很简单，只要再次通过bbed修复redolog文件头即可。
引用BBED> dump offset 0
File: /oradata/mynewdb/redo01.log (0)
Block: 1 Offsets: 0 to 511 Dba:0x00000000
------------------------------------
01220000 01000000 0a000000 00809db0 00000000 0002200a e28bcb0b 4d594e45
BBED> find 0x0002200a
File: /oradata/mynewdb/redo01.log (0)
Block: 1 Offsets: 20 to 511 Dba:0x00000000
------------------------------------
0002200a e28bcb0b 4d594e45 57444200 69000000 00200300 00020000 01000200
但由于bbed工具不会再次计算redolog的checksum值，所以修改之后该日志文件头也处于了checksum error状态
引用BBED> sum apply
Check value for File 0, Block 1:
current = 0x0000, required = 0x0000
SQL> recover database using backup controlfile;
ORA-00279: change 823455 generated at 05/13/2011 12:05:45 needed for thread 1
ORA-00289: suggestion :
/ora10g/oracle/product/10.2.0/db_1/dbs/arch1_11_748203362.dbf
ORA-00280: change 823455 for thread 1 is in sequence #11
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
/oradata/mynewdb/redo01.log
ORA-00367: checksum error in log file header
ORA-00334: archived log: '/oradata/mynewdb/redo01.log'
其实Oracle 对checkvalue值的计算只是各个字节相对简单的与或运算，由于手头没有现成脚本，于是打算放弃使用该redolog，强制启用Oracle。
启用隐含参数_allow_resetlogs_corruption
引用SQL> alter system set "_allow_resetlogs_corruption"=true scope=spfile;
System altered.
SQL> startup force mount
ORACLE instance started.
Total System Global Area 524288000 bytes
Fixed Size 1262716 bytes
Variable Size 180358020 bytes
Database Buffers 335544320 bytes
Redo Buffers 7122944 bytes
Database mounted.
SQL> recover database using backup controlfile until cancel;
ORA-00279: change 823455 generated at 05/13/2011 12:05:45 needed for thread 1
ORA-00289: suggestion : /ora10g/oracle/product/10.2.0/db_1/dbs/arch1_11_748203362.dbf
ORA-00280: change 823455 for thread 1 is in sequence #11
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below
ORA-01194: file 1 needs more recovery to be consistent
ORA-01110: data file 1: '/oradata/mynewdb/system01.dbf'
ORA-01112: media recovery not started
用reselogs选项打开Oracle。
引用
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01092: ORACLE instance terminated. Disconnection forced
实例异常终止，打开后台alert日志一看，2662错误如期而至
引用Fri May 13 12:29:00 2011
Errors in file /ora10g/oracle/product/10.2.0/db_1/rdbms/log/mynewdb_ora_22033.trc:
ORA-00600: internal error code, arguments: [2662], [0], [823461], [0], [823504], [4194313], [], []
Fri May 13 12:29:01 2011
Errors in file /ora10g/oracle/product/10.2.0/db_1/rdbms/log/mynewdb_ora_22033.trc:
ORA-00600: internal error code, arguments: [2662], [0], [823461], [0], [823504], [4194313], [], []
Fri May 13 12:29:01 2011
Error 600 happened during db open, shutting down database
USER: terminating instance due to error 600
Instance terminated by USER, pid = 22033
ORA-1092 signalled during: alter database open resetlogs..
ORA-600 [2662]主要是由于Oracle内部block的scn大于当前打开数据库的scn而引起的，主要有5个参数：
引用ERROR:
ORA-600 [2662] [a] [b] [c] [d] [e]
VERSIONS:
versions 6.0 to 10.1
DESCRIPTION:
A data block SCN is ahead of the current SCN.
The ORA-600 [2662] occurs when an SCN is compared to the dependent SCN
stored in a UGA variable.
If the SCN is less than the dependent SCN then we signal the ORA-600 [2662]
internal error.
ARGUMENTS:
Arg [a] Current SCN WRAP
Arg [b] Current SCN BASE
Arg [c] dependent SCN WRAP
Arg [d] dependent SCN BASE
Arg [e] Where present this is the DBA where the dependent SCN came from.
一般情况下，产生ora-600 [2662],可以通过设置event 10015事件，手工递增scn，即数据库open时的scn。
event 10015事件设置需要针对每个场景计算出level 1，通过2662几个参数根据一定的规则可以计算出我们需要的level。
计算规则如下：
Arg [c]*4得出一个数值，假设为V_Wrap
如果Arg [d]=0，则V_Wrap值为需要的level
Arg [d] < 1073741824，V_Wrap+1为需要的level
Arg [d] < 2147483648，V_Wrap+2为需要的level
Arg [d] < 3221225472，V_Wrap+3为需要的level
本案例中[c]=0，所以level为0*4+1=1，即在数据mount状态下，设置如下参数即可
引用SQL> ALTER SESSION SET EVENTS '10015 TRACE NAME ADJUST_SCN LEVEL 1';
Session altered.
但Oracle并不识别此event的设置，即并不递增scn值，在打开时，数据库依然报错
引用Fri May 13 12:45:09 2011
SMON: enabling cache recovery
Fri May 13 12:45:09 2011
Errors in file /ora10g/oracle/product/10.2.0/db_1/rdbms/log/mynewdb_ora_25610.trc:
ORA-00600: internal error code, arguments: [2662], [0], [823467], [0], [823504], [4194313], [], []
Fri May 13 12:45:09 2011
Errors in file /ora10g/oracle/product/10.2.0/db_1/rdbms/log/mynewdb_ora_25610.trc:
ORA-00600: internal error code, arguments: [2662], [0], [823467], [0], [823504], [4194313], [], []
Fri May 13 12:45:09 2011
也是尝试采用隐含参数_minimum_giga_scn，其取值方法和10015 event相同
引用SQL> alter system set "_minimum_giga_scn"=1 scope=spfile;
System altered.
再次尝试打开数据终于成功
引用SQL> recover database using backup controlfile until cancel;
ORA-00279: change 823463 generated at 05/13/2011 12:45:09 needed for thread 1
ORA-00289: suggestion :
/ora10g/oracle/product/10.2.0/db_1/dbs/arch1_1_751034707.dbf
ORA-00280: change 823463 for thread 1 is in sequence #1
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below
ORA-01194: file 1 needs more recovery to be consistent
ORA-01110: data file 1: '/oradata/mynewdb/system01.dbf'
ORA-01112: media recovery not started
SQL> alter database open resetlogs;
Database altered.
后台alert日志显示，scn已经递增成功。
引用Fri May 13 12:47:37 2011
alter database open resetlogs
Fri May 13 12:47:37 2011
RESETLOGS is being done without consistancy checks. This may result
in a corrupted database. The database should be recreated.
RESETLOGS after incomplete recovery UNTIL CHANGE 823463
Resetting resetlogs activation ID 200680610 (0xbf624a2)
Online log /oradata/mynewdb/redo01.log: Thread 1 Group 1 was previously cleared
Online log /oradata/mynewdb/redo02.log: Thread 1 Group 2 was previously cleared
Fri May 13 12:47:39 2011
Setting recovery target incarnation to 6
Fri May 13 12:47:39 2011
引用Advancing SCN to 1073741824 according to _minimum_giga_scn
Fri May 13 12:47:39 2011
Assigning activation ID 200679734 (0xbf62136)
Thread 1 opened at log sequence 1
Current log# 3 seq# 1 mem# 0: /oradata/mynewdb/redo03.log
Successful open of redo thread 1
Fri May 13 12:47:39 2011
MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set
Fri May 13 12:47:39 2011
SMON: enabling cache recovery
Fri May 13 12:47:39 2011
Successfully onlined Undo Tablespace 1.
Dictionary check beginning
Tablespace 'TEMPTS1' #3 found in data dictionary,
but not in the controlfile. Adding to controlfile.
Dictionary check complete
Fri May 13 12:47:39 2011
SMON: enabling tx recovery
Fri May 13 12:47:39 2011
*********************************************************************
WARNING: The following temporary tablespaces contain no files.
This condition can occur when a backup controlfile has
been restored. It may be necessary to add files to these
tablespaces. That can be done using the SQL statement:
ALTER TABLESPACE <tablespace_name> ADD TEMPFILE
Alternatively, if these temporary tablespaces are no longer
needed, then they can be dropped.
Empty temporary tablespace: TEMPTS1
*********************************************************************
Database Characterset is ZHS16GBK
replication_dependency_tracking turned off (no async multimaster replication found)
Starting background process QMNC
QMNC started with pid=16, OS id=401
Fri May 13 12:47:39 2011
LOGSTDBY: Validating controlfile with logical metadata
Fri May 13 12:47:39 2011
LOGSTDBY: Validation complete
Completed: alter database open resetlogs
可以看到数据库已经成功降级
引用SQL> show parameter compatible
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
compatible string 10.2.0.1.0
