来测试以下系统表OBJ$ 有坏块时的场景，数据库是否可以自动修复坏块？
（一）数据库环境
# 数据库版本
sys@ORCL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production
# 数据库运行状态
sys@ORCL> select dbid,current_scn,RESETLOGS_CHANGE#,flashback_on from v$database;
DBID CURRENT_SCN RESETLOGS_CHANGE# FLASHBACK_ON
---------- ----------- ----------------- ------------------
1520403684 3039036 2917000 YES
# DG同步状态
DGMGRL> show configuration
Configuration - orcl
Protection Mode: MaxPerformance
Databases:
orcl - Primary database
standby - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS
# 备库同步状态
SQL> select archived,max(sequence#),applied from v$archived_log group by archived,applied;
ARC MAX(SEQUENCE#) APPLIED
--- -------------- ---------
YES 24 IN-MEMORY
（二）还是保持隐含参数_auto_bmr 开启状态
col NAME for a30
col VALUE for a30
col describ for a40
SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ FROM x$ksppi x,x$ksppcv y
WHERE x.inst_id = USERENV ('Instance')
AND y.inst_id = USERENV ('Instance')
AND x.indx = y.indx
AND x.ksppinm LIKE '%_auto_bmr%';
NAME VALUE DESCRIB
------------------------------ ------------------------------ ----------------------------------------
_auto_bmr ENABLED enable/disable Auto BMR
_auto_bmr_req_timeout 60 Auto BMR Requester Timeout
_auto_bmr_sess_threshold 30 Auto BMR Request Session Threshold
_auto_bmr_pub_timeout 10 Auto BMR Publish Timeout
_auto_bmr_fc_time 60 Auto BMR Flood Control Time
_auto_bmr_bg_time 3600 Auto BMR Process Run Time
_auto_bmr_sys_threshold 100 Auto BMR Request System Threshold
_auto_bmr_max_rowno 1024 x$krbabrstat Max number of rows
8 rows selected.（三）备份数据库
RMAN> backup database;（四）查看对象OBJ$的segment状态
sys@ORCL> select segment_name,header_file , header_block,blocks from dba_segments where OWNER ='SYS' and segment_name ='OBJ$';
SEGMENT_NAME HEADER_FILE HEADER_BLOCK BLOCKS
--------------------------------------------------------------------------------- ----------- ------------ ----------
OBJ$ 1 240 1152（五）搞破坏，并强制重启数据库
dd if=/dev/zero of=/u01/app/oracle/oradata/standby/datafile/system01.dbf bs=8192 seek=240 count=2 conv=notrunc
2+0 records in
2+0 records out
16384 bytes (16 kB) copied, 0.000247249 s, 66.3 MB/s
sys@ORCL> shutdown abort
sys@ORCL> startup
Database mounted.
ORA-01092: ORACLE instance terminated. Disconnection forced
ORA-00704: bootstrap process failure
ORA-00704: bootstrap process failure
ORA-00604: error occurred at recursive SQL level 1
ORA-01578: ORACLE data block corrupted (file # 1, block # 241)
ORA-01110: data file 1: '/u01/app/oracle/oradata/standby/datafile/system01.dbf'
Process ID: 533
Session ID: 5 Serial number: 3
（六）使用RMAN验证数据文件状态
# 启动到mount状态
idle> startup mount
ORACLE instance started.
Total System Global Area 2455228416 bytes
Fixed Size 2255712 bytes
Variable Size 620758176 bytes
Database Buffers 1811939328 bytes
Redo Buffers 20275200 bytes
Database mounted.
# 使用RMAN验证文件状态
RMAN> backup validate database datafile 1;
idle> select * from v$database_block_corruption;
FILE# BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTIO
---------- ---------- ---------- ------------------ ---------
1 240 2 0 ALL ZERO
（七）修复并打开数据库
# 修复数据块
RMAN> blockrecover datafile 1 block 241;
Starting recover at 08-DEC-18
using channel ORA_DISK_1
searching flashback logs for block images until SCN 3125428
finished flashback log search, restored 1 blocks
starting media recovery
media recovery complete, elapsed time: 00:00:01
Finished recover at 08-DEC-18
# 打开数据库
idle> alter database open;
Database altered.
# 查询坏块已经被修复
idle> select * from v$database_block_corruption;
no rows selected若遇到数据库坏块启动不了的问题，先检查下坏块的是什么对象，若是系统表，就可以利用RMAN进行修复；若是索引则可以考虑删除或者重建；
备份很重要。
在这个测试场景中，还可以直接闪回数据库到正常状态。
