93. Your database is having two control files, three redo log file groups with two members

in each group. Failure of which file would cause an instance to shut down?
A) any control file
B) any archive log file
C) one of the redo log members
D) loss of the initialization parameter file
E) any data file belonging to the default permanent tablespace

1,修改control file 数量从默认的3个变为 题中描述的2个。
[oracle@test ~]$ sqlplus / as sysdba

SQL> show parameter db_name; #看下是那个数据库

NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
db_name string gzy
SQL> create pfile from spfile;

File created.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.

2，修改pfile 文件，在第三个control file 前加‘#’屏蔽它。
[root@test gzy]# cd /opt/ora10g/product/dbs/
[root@test dbs]# vi initgzy.ora

gzy.__db_cache_size=134217728
gzy.__java_pool_size=4194304
gzy.__large_pool_size=4194304
gzy.__shared_pool_size=113246208
gzy.__streams_pool_size=0
*.audit_file_dest='/opt/ora10g/admin/gzy/adump'
*.background_dump_dest='/opt/ora10g/admin/gzy/bdump'
*.compatible='10.2.0.1.0'
*.control_files='/opt/ora10g/oradata/gzy/gzy/control01.ctl','/opt/ora10g/oradata/gzy/gzy/co

ntrol02.ctl',
#'/opt/ora10g/oradata/gzy/gzy/control03.ctl'
*.core_dump_dest='/opt/ora10g/admin/gzy/cdump'
*.db_block_size=8192
*.db_domain=''
*.db_file_multiblock_read_count=16
*.db_name='gzy'
*.db_recovery_file_dest='/opt/ora10g/flash_recovery_area'
*.db_recovery_file_dest_size=10737418240
*.dispatchers='(PROTOCOL=TCP) (SERVICE=gzyXDB)'
*.job_queue_processes=10
*.lock_sga=TRUE
*.log_archive_format='%t_%s_%r.dbf'
*.open_cursors=300
*.pga_aggregate_target=307232768
*.pre_page_sga=TRUE
*.processes=150
*.remote_login_passwordfile='EXCLUSIVE'
*.sga_max_size=524288000
*.sga_target=264241152
*.undo_management='AUTO'
*.undo_tablespace='UNDOTBS1'
*.user_dump_dest='/opt/ora10g/admin/gzy/udump'

3，重新启动数据库，并确认 control file的数量；
SQL> startup
ORACLE instance started.

Total System Global Area 524288000 bytes
Fixed Size 1220384 bytes
Variable Size 381681888 bytes
Database Buffers 134217728 bytes
Redo Buffers 7168000 bytes
Database mounted.
Database opened.
SQL> show parameter control

NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
control_file_record_keep_time integer 7
control_files string /opt/ora10g/oradata/gzy/gzy/co
ntrol01.ctl, /opt/ora10g/orada
ta/gzy/gzy/control02.ctl
SQL> show parameter pfile #值为空，表明用的是pfile启动的数据库。

NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
spfile string
SQL> show parameter spfile

NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
spfile string
SQL>

4，在数据库OPEN的状态下，将2个control file 中的一个 改名；
[root@test gzy]# pwd
/opt/ora10g/oradata/gzy/gzy
[root@test gzy]# ll
total 1757068
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:02 control01.ctl
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:02 control02.ctl
-rw-r----- 1 oracle oinstall 7094272 Apr 1 15:52 control03.ctl
-rw-r----- 1 oracle oinstall 52429312 Apr 1 16:02 redo01.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 15:53 redo02.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 15:53 redo03.log
-rw-r----- 1 oracle oinstall 346038272 Apr 1 16:00 sysaux01.dbf
-rw-r----- 1 oracle oinstall 513810432 Apr 1 15:58 system01.dbf
-rw-r----- 1 oracle oinstall 513810432 Feb 8 12:22 system01.dbf.2
-rw-r----- 1 oracle oinstall 20979712 Apr 1 10:26 temp01.dbf
-rw-r----- 1 oracle oinstall 52436992 Apr 1 15:53 test01.dbf
-rw-r----- 1 oracle oinstall 10493952 Apr 1 15:53 test02.dbf
-rw-r----- 1 oracle oinstall 83894272 Apr 1 16:00 undotbs01.dbf
-rw-r----- 1 oracle oinstall 97001472 Apr 1 15:53 users01.dbf


[root@test gzy]# mv control02.ctl control02.ctl.bk
[root@test gzy]#
[root@test gzy]#
[root@test gzy]#
[root@test gzy]# ll
total 1757068
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:02 control01.ctl
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:02 control02.ctl.bk
-rw-r----- 1 oracle oinstall 7094272 Apr 1 15:52 control03.ctl
-rw-r----- 1 oracle oinstall 52429312 Apr 1 16:02 redo01.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 15:53 redo02.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 15:53 redo03.log
-rw-r----- 1 oracle oinstall 346038272 Apr 1 16:02 sysaux01.dbf
-rw-r----- 1 oracle oinstall 513810432 Apr 1 15:58 system01.dbf
-rw-r----- 1 oracle oinstall 513810432 Feb 8 12:22 system01.dbf.2
-rw-r----- 1 oracle oinstall 20979712 Apr 1 10:26 temp01.dbf
-rw-r----- 1 oracle oinstall 52436992 Apr 1 15:53 test01.dbf
-rw-r----- 1 oracle oinstall 10493952 Apr 1 15:53 test02.dbf
-rw-r----- 1 oracle oinstall 83894272 Apr 1 16:00 undotbs01.dbf
-rw-r----- 1 oracle oinstall 97001472 Apr 1 15:53 users01.dbf

SQL> desc tt; 可以查询，数据库正常运行中。
Name Null?

Type
----------------------------------------------------------------------------------- -----

--- --------------------------------------------------------
ID

NUMBER(38)
NAME

VARCHAR2(10)


数据库OPEN状态下，control丢失是没有问题的。

再看下，关闭再打开会发生什么？
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> statup
SP2-0042: unknown command "statup" - rest of line ignored.
SQL> startup
ORACLE instance started.

Total System Global Area 524288000 bytes
Fixed Size 1220384 bytes
Variable Size 381681888 bytes
Database Buffers 134217728 bytes
Redo Buffers 7168000 bytes
ORA-00205: error in identifying control file, check alert log for more info

SQL> select status from v$instance;

STATUS
------------------------
STARTED

[root@test gzy]# mv control02.ctl.bk control02.ctl

SQL> alter database open;

Database altered.

SQL> select status from v$instance;

STATUS
------------------------
OPEN


将所有的control file 全部改名；
[root@test gzy]# mv control03.ctl control03.ctl.bk
[root@test gzy]# ll
total 1757068
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:09 control01.ctl.bk
-rw-r----- 1 oracle oinstall 7094272 Apr 1 16:09 control02.ctl.bk
-rw-r----- 1 oracle oinstall 7094272 Apr 1 15:52 control03.ctl.bk
-rw-r----- 1 oracle oinstall 52429312 Apr 1 16:09 redo01.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 16:08 redo02.log
-rw-r----- 1 oracle oinstall 52429312 Apr 1 16:08 redo03.log
-rw-r----- 1 oracle oinstall 346038272 Apr 1 16:09 sysaux01.dbf
-rw-r----- 1 oracle oinstall 513810432 Apr 1 16:09 system01.dbf
-rw-r----- 1 oracle oinstall 513810432 Feb 8 12:22 system01.dbf.2
-rw-r----- 1 oracle oinstall 20979712 Apr 1 10:26 temp01.dbf
-rw-r----- 1 oracle oinstall 52436992 Apr 1 16:08 test01.dbf
-rw-r----- 1 oracle oinstall 10493952 Apr 1 16:08 test02.dbf
-rw-r----- 1 oracle oinstall 83894272 Apr 1 16:09 undotbs01.dbf
-rw-r----- 1 oracle oinstall 97001472 Apr 1 16:08 users01.dbf

查看control 的SCN信息；
SQL> select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
1 3471461
2 3471461
3 3471461
4 3471461
5 3471461
6 3471461
7 3472018

SQL> alter system checkpoint;

System altered.


SQL> select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
1 3474724
2 3474724
3 3474724
4 3474724
5 3474724
6 3474724
7 3474724

7 rows selected.

control file 的SCN变大了。但是control已经被改名了。
说明ORACLE还是能读写 control文件的。为什么。
上GOOGLE。

http://www.oracledatabase12g.com/archives/unix-linux%E4%B8%8B%E5%88%A0%E9%99%A4oracle%E6%8E%A7%E5%88%B6%E6%96%87%E4%BB%B6controlfile%E4%B8%BA%E4%BB%80%E4%B9%88%E5%AE%9E%E4%BE%8Binstance%E6%B2%A1%E6%9C%89%E7%AB%8B%E5%8D%B3%E5%A5%94%E6%BA%83.html

究其根本原因是在Linux/Unix上Read 或 Write一个文件，进程都会打开一个与此文件相关联的 打开文件描述符 Open File Descriptors (a file descriptor (FD) is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems.In POSIX, a file descriptor is an integer, specifically of the C type int.)

而在Linux/Unix上当一个文件被删除时，它只是简单地被”unlink”即删除一个硬链接hard link； 实际包含 文件数据的inode 在所有与该文件关联的 打开文件描述符(Open File Descriptors)被关闭之前 都不会被实际删除， 已经获得 打开文件描述符的进程 只要不用close函数关闭掉这些描述符， 都可以继续正常地对文件进行读写。 当所有该文件 管理的 打开文件符都被 关闭时 文件才真正意义上被删除。

总结，采用改名来模拟 control file文件存储介质损坏是不完善的。
可以采用，将control file 所在的磁盘的数据线直接拔掉来模拟。
请大家期待。。。





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