删除Oracle Online Redo 测试

删除Oracle Online Redo 测试
SQL> select * from v$log;
​
    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- ---------- --- --------
         1          1          4   52428800        512          1 NO  CURRENT
         2          1          2   52428800        512          1 NO  INACTIVE
         3          1          3   52428800        512          1 NO  INACTIVE
删除在线日志
SQL> !rm -rf  /u01/app/oracle/oradata/orcl11g/redo0*
​
SQL> !ls -l  /u01/app/oracle/oradata/orcl11g/redo0*
ls: cannot access /u01/app/oracle/oradata/orcl11g/redo0*: No such file or directory
​
SQL> quit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@cym1 trace]$ ll  /u01/app/oracle/oradata/orcl11g/redo*
ls: cannot access /u01/app/oracle/oradata/orcl11g/redo*: No such file or directory
查看删除日志后对数据库操作的影响：
SQL> alter system switch logfile;
​
System altered.
​
SQL> /
​
System altered.
​
....
SQL> select * from v$log;
​
    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARC STATUS          
---------- ---------- ---------- ---------- ---------- ---------- --- ----------------
         1          1         10   52428800        512          1 NO  INACTIVE        
         2          1         11   52428800        512          1 NO  INACTIVE        
         3          1         12   52428800        512          1 NO  CURRENT         
​
SQL> select * from v$logfile;
​
    GROUP# STATUS  TYPE    MEMBER                                             IS_
---------- ------- ------- -------------------------------------------------- ---
         2         ONLINE  /u01/app/oracle/oradata/orcl11g/redo02.log         NO
         3         ONLINE  /u01/app/oracle/oradata/orcl11g/redo03.log         NO
         1         ONLINE  /u01/app/oracle/oradata/orcl11g/redo01.log         NO
​
​
SQL> alter system switch logfile;
​
System altered.
​
SQL> alter system switch logfile;
​
System altered.
​
SQL> select * from v$log;
​
    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARC STATUS         
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------
         1          1         13   52428800        512          1 NO  INACTIVE       
         2          1         14   52428800        512          1 NO  CURRENT        
         3          1         12   52428800        512          1 NO  INACTIVE       
​
可见删除在线日志不影响数据库正常操作。

对数据库启动关闭的影响：
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup nomount;
ORACLE instance started.
​
Total System Global Area  409194496 bytes
Fixed Size                  2253744 bytes
Variable Size             310381648 bytes
Database Buffers           92274688 bytes
Redo Buffers                4284416 bytes
SQL> alter database mount;
​
Database altered.
​
SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel
Process ID: 76747
Session ID: 1 Serial number: 3
​
--查看日志
alter database open
Errors in file /u01/app/oracle/diag/rdbms/orcl11g/orcl11g/trace/orcl11g_lgwr_76732.trc:
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/orcl11g/redo01.log'
ORA-27037: unable to obtain file status
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3
Errors in file /u01/app/oracle/diag/rdbms/orcl11g/orcl11g/trace/orcl11g_lgwr_76732.trc:
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/orcl11g/redo01.log'
ORA-27037: unable to obtain file status
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3
Errors in file /u01/app/oracle/diag/rdbms/orcl11g/orcl11g/trace/orcl11g_ora_76747.trc:
ORA-00313: open failed for members of log group 1 of thread 
ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/orcl11g/redo01.log'
USER (ospid: 76747): terminating the instance due to error 313
​
因为日志文件丢失，启动三次失败后终止实例。
可见，删除在线日志后数据库可以正常关闭，但却不能正常启动，
下面进行恢复
[oracle@cym1 trace]$ rman target /
​
Recovery Manager: Release 11.2.0.4.0 - Production on Mon Feb 26 04:57:55 2018
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
connected to target database: ORCL11G (DBID=1057360211, not open)
​
RMAN> alter database open resetlogs;
​
using target database control file instead of recovery catalog
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of alter db command at 02/26/2018 04:58:18
ORA-01139: RESETLOGS option only valid after an incomplete database recovery
​
RMAN> recover database;
​
Starting recover at 2018-02-26 04:58:48
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:00
Finished recover at 2018-02-26 04:58:49
​
RMAN> alter database open resetlogs;
​
database opened
​
RMAN> quit
​
Recovery Manager complete.
​
[oracle@cym1 trace]$ sqlplus / as sysdba
​
SQL*Plus: Release 11.2.0.4.0 Production on Mon Feb 26 04:59:00 2018
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
​
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
​
SQL> select * from v$log;
​
    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE    MEMBERS ARC STATUS           
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- 
         1          1          1   52428800        512          1 NO  CURRENT          
         2          1          0   52428800        512          1 YES UNUSED           
         3          1          0   52428800        512          1 YES UNUSED           
​
SQL> select * from v$logfile;
​
    GROUP# STATUS  TYPE    MEMBER                                             IS_
---------- ------- ------- -------------------------------------------------- ---
         2         ONLINE  /u01/app/oracle/oradata/orcl11g/redo02.log         NO
         3         ONLINE  /u01/app/oracle/oradata/orcl11g/redo03.log         NO
         1         ONLINE  /u01/app/oracle/oradata/orcl11g/redo01.log         NO
​
SQL> quit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@cym1 trace]$ ll /u01/app/oracle/oradata/orcl11g/redo*
-rw-r----- 1 oracle oinstall 52429312 Feb 26 04:59 /u01/app/oracle/oradata/orcl11g/redo01.log
-rw-r----- 1 oracle oinstall 52429312 Feb 26 04:59 /u01/app/oracle/oradata/orcl11g/redo02.log
-rw-r----- 1 oracle oinstall 52429312 Feb 26 04:59 /u01/app/oracle/oradata/orcl11g/redo03.log
通过RestLogs 方式打开数据库后，恢复完成，在线日志文件已自行创建。

任何数据的变更数据库都会先记录redo,才能写到数据文件。但是redo 日志都丢了，怎么数据库还能正常操作呢？不应该直接宕机吗？
推测是因为Linux删除文件的机制导致，删除一个正在被使用的文件，Linux并没有真正删除它，关掉使用它的进程后，才会真正删除。

下面验证：
删除在线日志
[oracle@cym1 ~]$ rm -rf /u01/app/oracle/oradata/orcl11g/redo0*
[oracle@cym1 ~]$ ll /u01/app/oracle/oradata/orcl11g/redo*
ls: cannot access /u01/app/oracle/oradata/orcl11g/redo*: No such file or directory
[oracle@cym1 ~]$ sqlplus / as sysdba
​
SQL*Plus: Release 11.2.0.4.0 Production on Mon Feb 26 05:27:15 2018
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
​
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
​
SQL> select group#,thread#,sequence#,status from v$log;
​
    GROUP#    THREAD#  SEQUENCE# STATUS
---------- ---------- ---------- ----------------
         1          1          1 ACTIVE
         2          1          2 ACTIVE
         3          1          3 CURRENT
​
SQL> alter system switch logfile;
​
System altered.
.....
SQL>  select group#,thread#,sequence#,status from v$log;
​
    GROUP#    THREAD#  SEQUENCE# STATUS
---------- ---------- ---------- ----------------
         1          1          7 ACTIVE
         2          1          8 CURRENT
         3          1          6 ACTIVE
​
SQL> 
2. lsof 检查
[oracle@cym1 ~]$ lsof -n | grep -i deleted
oracle    76779    oracle  258u      REG              253,0   52429312 800980 /u01/app/oracle/oradata/orcl11g/redo01.log (deleted)
oracle    76779    oracle  259u      REG              253,0   52429312 800981 /u01/app/oracle/oradata/orcl11g/redo02.log (deleted)
oracle    76779    oracle  260u      REG              253,0   52429312 800982 /u01/app/oracle/oradata/orcl11g/redo03.log (deleted)
lsof 用来查看操作系统上被打开的文件，从以上来看在线日志文件仍然处于打开状态，说明还未被真正删除。
进程ID为 76779，下面查看日志文件在操作系统上的真正位置：
[oracle@cym1 ~]$ cd /proc/76779/fd
[oracle@cym1 fd]$ ls
0  1  10  11  12  13  14  2  256  257  258  259  260  261  262  263  264  265  266  267  268  3  4  5  6  7  8  9
[oracle@cym1 fd]$ ll
total 0
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 0 -> /dev/null
l-wx------ 1 oracle oinstall 64 Feb 26 05:29 1 -> /dev/null
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 10 -> /u01/app/oracle/product/11.2.0/dbhome_1/dbs/lkORCL11G
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 11 -> /u01/app/oracle/product/11.2.0/dbhome_1/rdbms/mesg/oraus.msb
l-wx------ 1 oracle oinstall 64 Feb 26 05:29 12 -> /u01/app/oracle/diag/rdbms/orcl11g/orcl11g/trace/orcl11g_lgwr_76779.trc
l-wx------ 1 oracle oinstall 64 Feb 26 05:29 13 -> /u01/app/oracle/diag/rdbms/orcl11g/orcl11g/trace/orcl11g_lgwr_76779.trm
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 14 -> socket:[748707]
l-wx------ 1 oracle oinstall 64 Feb 26 05:29 2 -> /dev/null
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 256 -> /u01/app/oracle/oradata/orcl11g/control01.ctl
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 257 -> /u01/app/oracle/fast_recovery_area/orcl11g/control02.ctl
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 258 -> /u01/app/oracle/oradata/orcl11g/redo01.log (deleted)
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 259 -> /u01/app/oracle/oradata/orcl11g/redo02.log (deleted)
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 260 -> /u01/app/oracle/oradata/orcl11g/redo03.log (deleted)
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 261 -> /u01/app/oracle/oradata/orcl11g/system01.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 262 -> /u01/app/oracle/oradata/orcl11g/sysaux01.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 263 -> /u01/app/oracle/oradata/orcl11g/undotbs01.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 264 -> /u01/app/oracle/oradata/orcl11g/users01.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 265 -> /u01/app/oracle/oradata/orcl11g/mgmt_depot.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 266 -> /u01/app/oracle/oradata/orcl11g/mgmt.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 267 -> /u01/app/oracle/oradata/orcl11g/mgmt_ad4j.dbf
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 268 -> /u01/app/oracle/oradata/orcl11g/temp01.dbf
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 3 -> /dev/null
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 4 -> /dev/null
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 5 -> /dev/null
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 6 -> /u01/app/oracle/product/11.2.0/dbhome_1/rdbms/mesg/oraus.msb
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 7 -> /proc/76779/fd
lr-x------ 1 oracle oinstall 64 Feb 26 05:29 8 -> /dev/zero
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 9 -> /u01/app/oracle/product/11.2.0/dbhome_1/dbs/hc_orcl11g.dat
可见在线日志对应的文件258/259/260还在，而且在数据库关闭前这3个资源是不会被释放的。这就解释了为什么删除在线日志文件不影响数据库正常操作。
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 258 -> /u01/app/oracle/oradata/orcl11g/redo01.log (deleted)
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 259 -> /u01/app/oracle/oradata/orcl11g/redo02.log (deleted)
lrwx------ 1 oracle oinstall 64 Feb 26 05:29 260 -> /u01/app/oracle/oradata/orcl11g/redo03.log (deleted)
下面关闭数据库，看看文件是不是被删除了
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> quit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@cym1 fd]$ ls
[oracle@cym1 fd]$ ll
total 0
[oracle@cym1 fd]$ cd ..
-bash: cd: ..: No such file or directory
[oracle@cym1 fd]$ ps -ef | grep 76779
oracle    77010  76395  0 05:39 pts/0    00:00:00 grep 76779
[oracle@cym1 fd]$ lsof -n | grep -i deleted
随着数据库实例的关闭，Oracle 进程76779消失，所有被Oracle占用的资源全部释放。导致Online Redolog彻底被删除，数据库也就不能启动了。