今天有客户的数据库意外被删除了整个目录中的数据文件，操作系统级别的删除，然而幸运的是这个数据库没有崩溃，仍然处于open状态
今天有客户的数据库意外被删除了整个目录中的数据文件，操作系统级别的删除，然而幸运的是这个数据库没有崩溃，，仍然处于open状态的时候，客户就发现了问题，求助到我们，最终完整地恢复了所有数据文件。
在Linux下大致重新演示一下恢复的过程，恢复的步骤与数据库版本没有太大关系，与操作系统的不同会有所不同。
1. 在数据库open的时候，直接删除users表空间中的数据文件。
SQL> select name from v$datafile; NAME -------------------------------------------------------------------------------- /app/Oracle/oradata/ORCL/datafile/o1_mf_system_555wqbnk_.dbf /app/oracle/oradata/ORCL/datafile/o1_mf_undotbs1_555wqxgl_.dbf /app/oracle/oradata/ORCL/datafile/o1_mf_sysaux_555wr5p6_.dbf /app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf SQL> host rm /app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf
2. 尝试在users表空间中创建表，开始报错。
SQL> create table t tablespace users as select * from dual; create table t tablespace users as select * from dual * ERROR at line 1: ORA-01116: error in opening database file 4 ORA-01110: data file 4: '/app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf' ORA-27041: unable to open file Linux Error: 2: No such file or directory Additional information: 3
在告警日志中，同样也可以看到类似信息。
Mon Dec 19 21:48:17 CST 2011 Errors in file /app/oracle/admin/orcl/bdump/orcl_m000_3897.trc: ORA-01116: error in opening database file 4 ORA-01110: data file 4: '/app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf' ORA-27041: unable to open file Linux Error: 2: No such file or directory Additional information: 3
3. 检查dbwr的进程PID
$ ps -ef|grep dbw0|grep -v grep oracle 2879 1 0 21:38 ? 00:00:00 ora_dbw0_orcl
4. dbwr会打开所有数据文件的句柄。在proc目录中可以查到，目录名是进程PID，fd表示文件描述符。
$ cd /proc/2879/fd $ ls -l total 0 lr-x------ 1 oracle dba 64 Dec 19 21:50 0 -> /dev/null lr-x------ 1 oracle dba 64 Dec 19 21:50 1 -> /dev/null lr-x------ 1 oracle dba 64 Dec 19 21:50 10 -> /dev/zero lr-x------ 1 oracle dba 64 Dec 19 21:50 11 -> /dev/zero lr-x------ 1 oracle dba 64 Dec 19 21:50 12 -> /app/oracle/product/10.2.0/db_1/rdbms/mesg/oraus.msb lrwx------ 1 oracle dba 64 Dec 19 21:50 13 -> /app/oracle/product/10.2.0/db_1/dbs/hc_orcl.dat lrwx------ 1 oracle dba 64 Dec 19 21:50 14 -> /app/oracle/product/10.2.0/db_1/dbs/lkORCL lrwx------ 1 oracle dba 64 Dec 19 21:50 15 -> /app/oracle/oradata/ORCL/controlfile/o1_mf_555wq3ng_.ctl lrwx------ 1 oracle dba 64 Dec 19 21:50 16 -> /app/oracle/oradata/ORCL/datafile/o1_mf_system_555wqbnk_.dbf lrwx------ 1 oracle dba 64 Dec 19 21:50 17 -> /app/oracle/oradata/ORCL/datafile/o1_mf_undotbs1_555wqxgl_.dbf lrwx------ 1 oracle dba 64 Dec 19 21:50 18 -> /app/oracle/oradata/ORCL/datafile/o1_mf_sysaux_555wr5p6_.dbf lrwx------ 1 oracle dba 64 Dec 19 21:50 19 -> /app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf (deleted) lr-x------ 1 oracle dba 64 Dec 19 21:50 2 -> /dev/null lrwx------ 1 oracle dba 64 Dec 19 21:50 20 -> /app/oracle/oradata/ORCL/datafile/o1_mf_temp_555wrbnz_.tmp lr-x------ 1 oracle dba 64 Dec 19 21:50 21 -> /app/oracle/product/10.2.0/db_1/rdbms/mesg/oraus.msb lr-x------ 1 oracle dba 64 Dec 19 21:50 3 -> /dev/null lr-x------ 1 oracle dba 64 Dec 19 21:50 4 -> /dev/null l-wx------ 1 oracle dba 64 Dec 19 21:50 5 -> /app/oracle/admin/orcl/udump/orcl_ora_2871.trc l-wx------ 1 oracle dba 64 Dec 19 21:50 6 -> /app/oracle/admin/orcl/bdump/alert_orcl.log lrwx------ 1 oracle dba 64 Dec 19 21:50 7 -> /app/oracle/product/10.2.0/db_1/dbs/lkinstorcl (deleted)
注意其中"/app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf (deleted)"字样，表示该文件已经被删除，如果是Solaris操作系统，ls命令不会有如此清晰的显示，为了在Solaris系统中确认哪个句 柄对应哪个文件，则需要使用lsof程序。
5. 直接cp该句柄文件名回原位置。
cp 19 /app/oracle/oradata/ORCL/datafile/o1_mf_users_555wrj4o_.dbf
6. 进行数据文件recover
SQL> alter database datafile 4 offline; Database altered. SQL> recover datafile 4; Media recovery complete. SQL> alter database datafile 4 online; Database altered.
完成数据文件恢复。
恢复的原理是，在Linux操作系统中，如果文件从操作系统级别被rm掉，之前打开该文件的进程仍然持有相应的文件句柄，所指向的文件仍然可以读 写，并且该文件的文件描述符可以从/proc目录中获得。但是要注意的是，此时如果关闭数据库，则此句柄会消失，那么除了扫描磁盘进行文件恢复之外就没有 其它方法了，因此在数据库出现问题的时候，如果不确认情况的复杂程度，千万不要随便关闭数据库。重启数据库往往是没有意义的，甚至是致命的。
当然，客户的操作系统是Solaris，并且客户删除的文件还包括current online redo log，因此还有其它更复杂的操作，不在这里描述。
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