对于Oracle数据块物理损坏的情形，在我们有备份的情况下可以直接使用备份来恢复。对于通过备份恢复，Oracel为我们提供了很多种方式，冷备，基于用户管理方式，RMAN方式等等。对于这几种方式我们需要实现基于数据库以及文件级别的恢复。RMAN同时也提供了基于块介质方式的恢复。也就是说我们根本不需要还原数据文件，而是直接从备份文件基于块来提取以实现联机恢复。可参考基于RMAN实现坏块介质恢复(blockrecover) 。这是比较理想的情形。如果没有任何备份怎么办？我们可以注意，不要被文章题目有所误导。这里的修复是有损修复也就是说将受损的数据块标记为坏块，不对其进行访问而已。就好比我们磁盘有坏道，找个磁盘修复工具将坏道标出来不使用，同理。那受损的数据岂不是无力回天啦，呜呜......要记得随时备份阿。。
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1、DBMS_REPAIR包所含的过程
Procedure_Name Description
----------------- ------------------------------------
ADMIN_TABLES Provides administrative functions (create, drop, purge) for repair or orphan key tables.
Note: These tables are always created in the SYS schema.
CHECK_OBJECT Detects and reports corruptions in a table or index
DUMP_ORPHAN_KEYS Reports on index entries that point to rows in corrupt data blocks
FIX_CORRUPT_BLOCKS Marks blocks as software corrupt that have been previously identified as corrupt by the CHECK_OBJECT procedure
REBUILD_FREELISTS Rebuilds the free lists of the object
SEGMENT_FIX_STATUS Provides the capability to fix the corrupted state of a bitmap entry when segment space management is AUTO
SKIP_CORRUPT_BLOCKS When used, ignores blocks marked corrupt during table and index scans.
If not used, you get error ORA-01578 when encountering blocks marked corrupt.
2、DBMS_REPAIR的一些局限性
Tables with LOB data types, nested tables, and varrays are supported, but the out-of-line columns are ignored.
Clusters are supported in the SKIP_CORRUPT_BLOCKS and REBUILD_FREELISTS procedures, but not in the CHECK_OBJECT procedure.
Index-organized tables and LOB indexes are not supported.
The DUMP_ORPHAN_KEYS procedure does not operate on bitmap indexes or function-based indexes.
The DUMP_ORPHAN_KEYS procedure processes keys that are no more than 3,950 bytes long.
3、创建演示环境
--当前环境
sys@USBO> select * from v$version where rownum create tablespace tbs_tmp datafile '/u02/database/usbo/oradata/tbs_tmp.dbf' size 10m autoextend on;
--创建表对象tb_obj及其索引
sys@USBO> create table tb_obj tablespace tbs_tmp as select * from dba_objects;
sys@USBO> create index i_tb_obj on tb_obj(object_id);
--表段上的相关信息
sys@USBO> select segment_name , header_file , header_block,blocks
2 from dba_segments where segment_name ='TB_OBJ';
SEGMENT_NAME HEADER_FILE HEADER_BLOCK BLOCKS
------------------------------ ----------- ------------ ----------
TB_OBJ 6 130 1152
--使用linux自带的dd命令来损坏数据块
[oracle@linux1 ~]$ dd of=/u02/database/usbo/oradata/tbs_tmp.dbf bs=8192 conv=notrunc seek=131 EOF
0+1 records in
0+1 records out
12 bytes (12 B) copied, 0.000209854 seconds, 57.2 kB/s
[oracle@linux1 ~]$ dd of=/u02/database/usbo/oradata/tbs_tmp.dbf bs=8192 conv=notrunc seek=141 EOF
0+1 records in
0+1 records out
12 bytes (12 B) copied, 0.00019939 seconds, 60.2 kB/s
[oracle@linux1 ~]$ dd of=/u02/database/usbo/oradata/tbs_tmp.dbf bs=8192 conv=notrunc seek=151 EOF
0+1 records in
0+1 records out
12 bytes (12 B) copied, 2.1672e-05 seconds, 554 kB/s
sys@USBO> alter system flush buffer_cache;
--下面的查询收到了错误提示
sys@USBO> select count(*) from tb_obj;
select count(*) from tb_obj
*
ERROR at line 1:
ORA-01578: ORACLE data block corrupted (file # 6, block # 131)
ORA-01110: data file 6: '/u02/database/usbo/oradata/tbs_tmp.dbf'