1.官方文档描述
关于Clearing a Redo Log File的官方文档描述：
> A redo log file might become corrupted while the database is open, and ultimately stop database activity because archiving cannot continue. In this situation the ALTER DATABASE CLEAR LOGFILE statement can be used to reinitialize the file without shutting down the database.
>
> The following statement clears the log files in redo log group number 3:
>
> ALTER DATABASE CLEAR LOGFILE GROUP 3;
> This statement overcomes two situations where dropping redo logs is not possible:
>
> If there are only two log groups
>
> The corrupt redo log file belongs to the current group
>
> If the corrupt redo log file has not been archived, use the UNARCHIVED keyword in the statement.
>
> ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;
> This statement clears the corrupted redo logs and avoids archiving them. The cleared redo logs are available for use even though they were not archived.
>
> If you clear a log file that is needed for recovery of a backup, then you can no longer recover from that backup. The database writes a message in the alert log describing the backups from which you cannot recover.
2.故障报错信息
启动数据库在open阶段失败：
SQL> startup
ORACLE instance started.
Total System Global Area 313860096 bytes
Fixed Size 1344652 bytes
Variable Size 205523828 bytes
Database Buffers 100663296 bytes
Redo Buffers 6328320 bytes
Database mounted.
ORA-03113: end-of-file on communication channel
Process ID: 2039
Session ID: 102 Serial number: 5
进一步查看alert告警日志发现是redo日志文件损坏：
Mon May 20 01:00:52 2019
alter database open
Mon May 20 01:00:52 2019
LGWR: STARTING ARCH PROCESSES
Mon May 20 01:00:53 2019
ARC0 started with pid=18, OS id=2389
ARC0: Archival started
LGWR: STARTING ARCH PROCESSES COMPLETE
ARC0: STARTING ARCH PROCESSES
Mon May 20 01:00:54 2019
ARC1 started with pid=19, OS id=2391
Mon May 20 01:00:54 2019
ARC2 started with pid=20, OS id=2393
Incomplete read from log member '/u03/oradata/PROD2/redo01.dbf'. Trying next member.
ARCH: All Archive destinations made inactive due to error 333
ARCH: Closing local archive destination LOG_ARCHIVE_DEST_1: '/u01/app/oracle/product/11.2.0/db_1/dbs/arch1_1_1008712962.dbf' (error 333) (PROD2)
Committing creation of archivelog '/u01/app/oracle/product/11.2.0/db_1/dbs/arch1_1_1008712962.dbf' (error 333)
Mon May 20 01:00:54 2019
ARC3 started with pid=21, OS id=2395
Errors in file /u01/app/oracle/diag/rdbms/prod2/PROD2/trace/PROD2_ora_2179.trc:
ORA-16038: log 1 sequence# 1 cannot be archived
ORA-00333: redo log read error block count
ORA-00312: online log 1 thread 1: '/u03/oradata/PROD2/redo01.dbf'
ARC1: Archival started
ARC2: Archival started
USER (ospid: 2179): terminating the instance due to error 16038
Mon May 20 01:00:55 2019
System state dump requested by (instance=1, osid=2179), summary=[abnormal instance termination].
System State dumped to trace file /u01/app/oracle/diag/rdbms/prod2/PROD2/trace/PROD2_diag_2131.trc
Dumping diagnostic data in directory=[cdmp_20190520010055], requested by (instance=1, osid=2179), summary=[abnormal instance termination].
Instance terminated by USER, pid = 2179
3.分析解决问题
**3.1 再次尝试启动数据库故障可重现**
SQL> startup mount;
SQL> select checkpoint_change# from v$datafile;
CHECKPOINT_CHANGE#
------------------
2126114
2126114
2126114
2126114
2126114
SQL> select checkpoint_change# from v$datafile_header;
CHECKPOINT_CHANGE#
------------------
2126114
2126114
2126114
2126114
2126114
SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel
Process ID: 2179
Session ID: 102 Serial number: 5
3.2 启动到mount尝试clear重做日志文件
SQL> conn /as sysdba
Connected to an idle instance.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 313860096 bytes
Fixed Size 1344652 bytes
Variable Size 205523828 bytes
Database Buffers 100663296 bytes
Redo Buffers 6328320 bytes
Database mounted.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 1 52428800 512 1 NO INACTIVE 2080429 19-MAY-19 2105566 20-MAY-19
3 1 3 52428800 512 1 NO CURRENT 2106113 20-MAY-19 2.8147E+14
2 1 2 52428800 512 1 NO INACTIVE 2105566 20-MAY-19 2106113 20-MAY-19
SQL> alter database clear logfile group 1;
alter database clear logfile group 1
*
ERROR at line 1:
ORA-00350: log 1 of instance PROD2 (thread 1) needs to be archived
ORA-00312: online log 1 thread 1: '/u03/oradata/PROD2/redo01.dbf'
SQL> alter database clear unarchived logfile group 1;
Database altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 0 52428800 512 1 YES UNUSED 2080429 19-MAY-19 2105566 20-MAY-19
3 1 3 52428800 512 1 NO CURRENT 2106113 20-MAY-19 2.8147E+14
2 1 2 52428800 512 1 NO INACTIVE 2105566 20-MAY-19 2106113 20-MAY-19
由于本次3个redo日志全部确认已损坏，需要依次clear:
SQL> alter database clear logfile group 2;
alter database clear logfile group 2
*
ERROR at line 1:
ORA-00350: log 2 of instance PROD2 (thread 1) needs to be archived
ORA-00312: online log 2 thread 1: '/u03/oradata/PROD2/redo02.dbf'
SQL> alter database clear logfile group 3;
alter database clear logfile group 3
*
ERROR at line 1:
ORA-00350: log 3 of instance PROD2 (thread 1) needs to be archived
ORA-00312: online log 3 thread 1: '/u03/oradata/PROD2/redo03.dbf'
SQL> alter database clear unarchived logfile group 2;
Database altered.
SQL> alter database clear unarchived logfile group 3;
Database altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 4 52428800 512 1 NO CURRENT 2106114 20-MAY-19 2.8147E+14
3 1 0 52428800 512 1 YES UNUSED 2106113 20-MAY-19 2106114 20-MAY-19
2 1 0 52428800 512 1 YES UNUSED 2105566 20-MAY-19 2106113 20-MAY-19
SQL> alter database open;
Database altered.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES BLOCKSIZE MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ ---------
1 1 4 52428800 512 1 NO CURRENT 2106114 20-MAY-19 2.8147E+14
2 1 0 52428800 512 1 YES UNUSED 2105566 20-MAY-19 2106113 20-MAY-19
3 1 0 52428800 512 1 YES UNUSED 2106113 20-MAY-19 2106114 20-MAY-19
数据库开启后建议尽快重新执行一次全备。