oracle通過日誌文件保證提交成功的數據不丟失,可是在故障中,用戶可能損失了當前的
(current)日誌文件.這又分爲兩種情況:此時數據是正常關閉的和此時數據庫是異常關閉.
1.在損失當前日誌時,數據庫是正常關閉的.
由於關閉數據庫前,oracle會執行全面檢查點,當前日誌在實例恢復中可以不再需要.
下面進行測試(數據庫運行在非歸檔模式下).在oracle9i及以後版本中,是無法對當前
日誌進行clear,需要通過until cancel恢復後再以resetlogs方式打開
[oracle@jingyong ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Mon Jan 7 00:39:59 2013
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> select * from v$version where rownum<2;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
SQL> select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
IS_
---
3 ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo03.log
NO
2 ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo02.log
NO
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
IS_
---
1 ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo01.log
NO
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> !mv /u01/app/oracle/product/10.2.0/oradata/jingyong/redo* /u01/app/oracle
SQL> startup
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 62916852 bytes
Database Buffers 100663296 bytes
Redo Buffers 2973696 bytes
Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1:
'/u01/app/oracle/product/10.2.0/oradata/jingyong/redo01.log'
SQL> alter database clear logfile group 1;
Database altered.
SQL> alter database clear logfile group 2;
Database altered.
SQL> alter database clear logfile group 3;
alter database clear logfile group 3
*
ERROR at line 1:
ORA-00313: open failed for members of log group 3 of thread 1
ORA-00312: online log 3 thread 1:
'/u01/app/oracle/product/10.2.0/oradata/jingyong/redo03.log'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIME
------------- ------------
1 1 0 52428800 1 NO UNUSED
0 06-JAN-13
3 1 0 52428800 1 NO CLEARING_CURRENT
914164 06-JAN-13
2 1 0 52428800 1 NO UNUSED
914157 06-JAN-13
SQL> recover database until cancel;
Media recovery complete.
SQL> alter database open resetlogs;
Database altered.
SQL>
2.在損失當前日誌,數據庫是異常關閉的
如果在損失當前日誌時,數據庫是異常關閉的,那麼oracle在進行實例恢復時必須要求當前日誌,
否則oracle將無法保證提交成功的數據不丟失(也就是意味着oracle會丟失數據),在這種情況下,
oracle數據庫將無法啓動.
對於這種情況,通常需要從備份中恢復數據文件,通過應用歸檔日誌文件向前推演,直到最後一個
完好的日誌文件,然後可以通過resetlogs啓動數據庫完成恢復.丟失的數據就是損壞的日誌文件
中的數據.
如果沒有備份,oracle有一類具有特殊作用的隱含參數,其中一個參數是_allow_resetlogs_corruption,來看一下
這個參數的說明:
SQL> select x.ksppinm NAME,y.ksppstvl value,x.ksppdesc describ
2 from x$ksppi x, x$ksppcv y
3 where x.inst_id=USERENV('Instance')
4 and y.inst_id=USERENV('Instance')
5 and x.indx=y.indx
6 and x.ksppinm like '%_allow_resetlogs_%';
NAME VALUE DESCRIB
------------------------------ -------------- --------------------------------------------------
_allow_resetlogs_corruption FALSE allow resetlogs even if it will cause corruption
該參數的含義是,允許在破壞一致性的情況下強制重置日誌,打開數據庫._allow_resetlogs_corruption將
使用所有數據文件中最舊的scn打開數據庫,所以通常需要保證system表空間擁有最舊的scn.
在強制打開數據庫之後,可能因爲各種原因伴隨出現ora-00600錯誤,有些可以依據常規途徑解決,看一下下面
的例子:
[oracle@jingyong ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Mon Jan 7 02:04:02 2013
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
查詢當前的日誌組
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIME
------------- ------------
1 1 2 52428800 1 NO CURRENT
936058 07-JAN-13
2 1 0 52428800 1 YES UNUSED
0
3 1 1 52428800 1 NO INACTIVE
914918 07-JAN-13
SQL> select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
IS_
---
3 STALE ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo03.log
NO
2 ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo02.log
NO
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
IS_
---
1 ONLINE
/u01/app/oracle/product/10.2.0/oradata/jingyong/redo01.log
NO
刪除當前日誌組的日誌文件
SQL> !rm -rf /u01/app/oracle/product/10.2.0/oradata/jingyong/redo01.log
SQL> shutdown abort;
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 62916852 bytes
Database Buffers 100663296 bytes
Redo Buffers 2973696 bytes
Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1:
'/u01/app/oracle/product/10.2.0/oradata/jingyong/redo01.log'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
啓動失敗,日誌文件損壞,在mount狀態,可以查詢v$log視圖,發現此處損壞的是current的日誌文件
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIME
------------- ------------
1 1 2 52428800 1 NO CURRENT
936058 07-JAN-13
3 1 1 52428800 1 NO INACTIVE
914918 07-JAN-13
2 1 0 52428800 1 YES UNUSED
0
SQL>
由於active和current日誌沒有完成檢查點，在恢復中需要用到,丟失active和current日誌情況類似.
如果沒有備份,只好使用隱含參數_allow_resetlogs_corruption強制啓動數據庫,設置此參數之後,
在數據庫open過程中,oracle會跳過某些一致性檢查,從而使用權數據庫可能跳過不一致狀態,直接打開.
SQL> alter system set "_allow_resetlogs_corruption"=true scope=spfile;
System altered.
SQL> shutdown
ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 167772160 bytes
Fixed Size 1218316 bytes
Variable Size 62916852 bytes
Database Buffers 100663296 bytes
Redo Buffers 2973696 bytes
Database mounted.
SQL> recover database until cancel;
ORA-00279: change 936059 generated at 01/07/2013 02:01:11 needed for thread 1
ORA-00289: suggestion :
/u01/app/oracle/product/10.2.0/flash_recovery_area/JINGYONG/archivelog/2013_01_0
7/o1_mf_1_2_%u_.arc
ORA-00280: change 936059 for thread 1 is in sequence #2
Specify log: {=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:
'/u01/app/oracle/product/10.2.0/oradata/jingyong/system01.dbf'
ORA-01112: media recovery not started
SQL> alter database open resetlogs;
Database altered.
SQL>
如果運氣好的話,數據庫就可以成功打開了,如果不幸,則可能會遇到一些ora-00600的錯誤
那麼就需要使用其它方法來進行恢復
通過這種方法恢復可以在alert日誌中看見類似以下的日誌信息:
Mon Jan 7 02:11:19 2013
alter database open resetlogs
Mon Jan 7 02:11:19 2013
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 936059
Resetting resetlogs activation ID 3141718551 (0xbb42d217)
Mon Jan 7 02:11:19 2013
不一致恢復最後恢復到的change號是936059,信息中說明了強制resetlogs不進行一致性檢查,
可能會導致數據庫損壞,數據庫應當重建.