在线修改online redo logfiles size 大小  
 
oracle redolog size 过小有时候会导致性能问题，现在我们在线修改redolog，一般在业务量比较小的时候进行此操作  
 
1. 首先查看当前的日志组大小，路径名             
                 
[oracle@tora10 ~]$ sqlplus / as sysdba  
 
SQL*Plus: Release 10.2.0.4.0 - Production on Sat Feb 23 17:08:33 2013  
 
SQL> select group#, bytes, status from v$log;   
 
    GROUP#      BYTES STATUS  
---------- ---------- ----------------  
         1  524288000 INACTIVE  
         2  524288000 CURRENT  
         3  524288000 INACTIVE  
           
    当前的日志组大小是 512MB 文件系统，每个组成员只有1个member                                
                                    
   SQL> select group#, member from v$logfile;                                      
                                                         
    GROUP# MEMBER  
---------- ----------------------------------------  
         1 /opt/oracle/oradata/test/redo01.log  
         2 /opt/oracle/oradata/test/redo02.log  
         3 /opt/oracle/oradata/test/redo03.log                                   
                                                                 
                                                                  
2. 现在创建新的redolog group 4, 5, and 6 每个log大小为1024MB                            
                              
   SQL> alter database add logfile group 4                                
           '/opt/oracle/oradata/test/redo04.log ' size 1024M;                                   
                                   
   SQL> alter database add logfile group 5                                    
           '/opt/oracle/oradata/test/redo05.log ' size 1024M;       
          
   SQL> alter database add logfile group 6            
           '/opt/oracle/oradata/test/redo06.log ' size 1024M;     
          
 
3. 创建完新的日志组后，查询所有日志组状态:                                     
                                                                           
   SQL> select group#, status from v$log;                                         
 
      GROUP# STATUS  
   --------- ----------------  
           1 INACTIVE  
           2 CURRENT  
           3 INACTIVE              
           4 UNUSED  
           5 UNUSED  
           6 UNUSED           
                         
   当前使用的是group 2 日志组，现在通过“多次”切日志换命令将group 1,2,3状态变为INACTIVE，  
让oracle使用新建的group4,5,6，然后将小的日志组group 1,2,3删除              
                                
      
   SQL> alter system switch logfile;            
                                        
   SQL> alter system checkpoint;                                                        
                                                                                                                         
4.切换完成后，再次查询当前的日志组状态，当前使用的日志组是group 5  
                                                                 
   SQL> select group#, status from v$log;                                         
                                                                           
             
      GROUP# STATUS  
     -------- ------  
         1 INACTIVE  
         2 INACTIVE  
         3 INACTIVE  
         4 INACTIVE  
         5 CURRENT  
         6 INACTIVE  
    当redolog group 1,2,3状态为active时，意味着不能删除当前redo,直至用"alter system switch log file" ，"alter system checkpoint"   
命令将其切换为“inactive”状态才能将其删除  
                         
                                                    
5.删除group 1,2,3日志组      
 
   SQL> alter database drop logfile group 1;    
        Database altered.                                    
   SQL> alter database drop logfile group 2;    
        Database altered.                                    
   SQL> alter database drop logfile group 3;    
        Database altered.                                    
                                     
 
   SQL> select group#, bytes, status from v$log;  
 
      GROUP#     BYTES STATUS  
   --------- --------- ----------------  
           4  10485760 CURRENT  
           5  10485760 UNUSED  
           6  10485760 UNUSED              
 
 
     
6.  整个操作完成后，最好做一个backup  
 
7.在操作系统层面删除原来的redolog  
      
[oracle@tora10 ~]$ cd /opt/oracle/oradata/test/  
[oracle@tora10 test]$ ll -al redo*  
-rw-r----- 1 oracle oinstall  524288512 Feb 23 17:15 redo01.log  
-rw-r----- 1 oracle oinstall  524288512 Feb 23 17:15 redo02.log  
-rw-r----- 1 oracle oinstall  524288512 Feb 23 17:15 redo03.log  
-rw-r----- 1 oracle oinstall 1073742336 Feb 23 17:16 redo04.log   
-rw-r----- 1 oracle oinstall 1073742336 Feb 23 17:16 redo05.log   
-rw-r----- 1 oracle oinstall 1073742336 Feb 23 17:17 redo06.log   
 
删除小的redolog  
 
[oracle@tora10 test]$ rm -rf redo01.log   
[oracle@tora10 test]$ rm -rf redo02.log   
[oracle@tora10 test]$ rm -rf redo03.log                                              
                                                    
 
值得注意的是，加完新的redolog group 后，要监控下alert log 查看新的redolog的切换频率与原来情况相比较