在很多情况下，数据库只是某个数据文件的些许数据块发生损坏。这种情况，我们当然可是使用数据库恢复或者数据文件恢复的方式来解决问题。但是有点高射炮打蚊子的感觉。幸好RMAN提供了块级别的恢复。下面我们来演示一下。
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1. 创建一个表空间，大小小一点。
SQL> conn / as sysdba Connected. SQL> create tablespace tbs_blkerr datafile '/u01/app/oracle/oradata/devdb/blkerr01.dbf' size 128K; Tablespace created.
2. 在这个表空间上创建一个表，并且装满数据。
SQL> create table emp_blk tablespace tbs_blkerr as select * from scott.emp; Table created. SQL> insert into emp_blk select * from scott.emp; 14 rows created. SQL> / 14 rows created. 。。。。 SQL> insert into emp_blk select * from scott.emp; insert into emp_blk select * from scott.emp * ERROR at line 1: ORA-01653: unable to extend table SYS.EMP_BLK by 8 in tablespace TBS_BLKERR SQL> commit; Commit complete. SQL> select count(*) from emp_blk; COUNT(*) ---------- 686 SQL>
3. 备份该表空间或者数据文件。
RMAN> backup datafile '/u01/app/oracle/oradata/devdb/blkerr01.dbf'; Starting backup at 2015/07/09 10:30:11 using channel ORA_DISK_1 channel ORA_DISK_1: starting full datafile backup set channel ORA_DISK_1: specifying datafile(s) in backup set input datafile file number=00007 name=/u01/app/oracle/oradata/devdb/blkerr01.dbf channel ORA_DISK_1: starting piece 1 at 2015/07/09 10:30:11 channel ORA_DISK_1: finished piece 1 at 2015/07/09 10:30:12 piece handle=/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_09/o1_mf_nnndf_TAG20150709T103011_bsvq5mw9_.bkp tag=TAG20150709T103011 comment=NONE channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01 Finished backup at 2015/07/09 10:30:12
4. 使用vi编辑数据文件blkerr01.dbf,对文件尾部做稍微的修改
SQL> shutdown immediate Database closed. Database dismounted. ORACLE instance shut down. SQL> startup ORACLE instance started. Total System Global Area 839282688 bytes Fixed Size 2233000 bytes Variable Size 553651544 bytes Database Buffers 281018368 bytes Redo Buffers 2379776 bytes Database mounted. ORA-01157: cannot identify/lock data file 7 - see DBWR trace file ORA-01110: data file 7: '/u01/app/oracle/oradata/devdb/blkerr01.dbf' RMAN> restore datafile 7; Starting restore at 2015/07/09 10:36:25 using target database control file instead of recovery catalog allocated channel: ORA_DISK_1 channel ORA_DISK_1: SID=20 device type=DISK channel ORA_DISK_1: starting datafile backup set restore channel ORA_DISK_1: specifying datafile(s) to restore from backup set channel ORA_DISK_1: restoring datafile 00007 to /u01/app/oracle/oradata/devdb/blkerr01.dbf channel ORA_DISK_1: reading from backup piece /u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_09/o1_mf_nnndf_TAG20150709T103011_bsvq5mw9_.bkp channel ORA_DISK_1: piece handle=/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_09/o1_mf_nnndf_TAG20150709T103011_bsvq5mw9_.bkp tag=TAG20150709T103011 channel ORA_DISK_1: restored backup piece 1 channel ORA_DISK_1: restore complete, elapsed time: 00:00:01 Finished restore at 2015/07/09 10:36:27 RMAN> recover datafile 7; Starting recover at 2015/07/09 10:36:40 using channel ORA_DISK_1 starting media recovery media recovery complete, elapsed time: 00:00:00 Finished recover at 2015/07/09 10:36:41
此次修改破坏了文件的头部，发生了意外。（也可能是编辑datafile时，没有关闭数据库）我们先恢复数据文件。再次编辑文件。
此实验始终没有做成功，后续有时间再研究。
恢复的方法如下：
RMAN TARGET / BLOCKRECOVER DATAFILE 12 BLOCK 12;
