????3???????????????С

sys@CNBO1> alter system archive log all;   -->?鵵??????????
alter system archive log all
*
ERROR at line 1:
ORA-00271: there are no logs that need archiving   -->???????????????й鵵     

sys@CNBO1> alter database drop logfile group 1;    -->????group1 ????active???????????
alter database drop logfile group 1
*
ERROR at line 1:                                   -->???????crash recovery?????
ORA-01624: log 1 needed for crash recovery of instance CNBO1 (thread 1)
ORA-00312: online log 1 thread 1: '/u02/database/CNBO1/redolog/log1aCNBO1.log'
ORA-00312: online log 1 thread 1: '/u02/database/CNBO1/redolog/log1bCNBO1.log'

sys@CNBO1> alter system switch logfile;            -->?л????

System altered.

sys@CNBO1> select group#??archived??status from v$log; -->???????????仯

    GROUP# ARC STATUS
---------- --- ----------------
         1 NO  CURRENT
         2 YES INACTIVE
         3 YES INACTIVE
         4 YES ACTIVE

sys@CNBO1> alter database drop logfile group 2;     -->?????2???????

Database altered.

sys@CNBO1> ho ls /u02/database/CNBO1/redolog/log2*  -->????????????????????б????
/u02/database/CNBO1/redolog/log2aCNBO1.log  /u02/database/CNBO1/redolog/log2bCNBO1.log            

sys@CNBO1> alter database add logfile group 2 ('/u02/database/CNBO1/redolog/log2aCNBO1.log'??
  2  '/u02/database/CNBO1/redolog/log2bCNBO1.log') size 100m reuse;   -->???????飬??????μ?size

Database altered.

sys@CNBO1> alter database drop logfile group 3;

Database altered.

sys@CNBO1> alter database add logfile group 3 ('/u02/database/CNBO1/redolog/log3aCNBO1.log'??
  2  '/u02/database/CNBO1/redolog/log3bCNBO1.log') size 100m reuse;

Database altered.

sys@CNBO1> select group#??archived??status from v$log;   -->????????????unused????
                                                       -->?????????????л????????????л???unused?????
    GROUP# ARC STATUS
---------- --- ----------------
         1 NO  CURRENT
         2 YES UNUSED
         3 YES UNUSED
         4 YES ACTIVE

sys@CNBO1> alter system switch logfile;

System altered.

-->?л?????????????????????????л??INACTIVE?????????????????
-->???????????????????????????????????????????
-->?????????????????С?????????
--> Author : Robinson
--> Blog   : http://blog.csdn.net/robinson_0612

sys@CNBO1> @log_stat

    GROUP# MEMBER                                         SEQUENCE#    SIZE_MB STATUS
---------- --------------------------------------------- ---------- ---------- -------
         1 /u02/database/CNBO1/redolog/log1aCNBO1.log          4893        100 CURRENT
         1 /u02/database/CNBO1/redolog/log1bCNBO1.log          4893        100 CURRENT
         2 /u02/database/CNBO1/redolog/log2aCNBO1.log          4890        100 INACTIVE
         2 /u02/database/CNBO1/redolog/log2bCNBO1.log          4890        100 INACTIVE
         3 /u02/database/CNBO1/redolog/log3aCNBO1.log          4891        100 INACTIVE
         3 /u02/database/CNBO1/redolog/log3bCNBO1.log          4891        100 INACTIVE
         4 /u02/database/CNBO1/redolog/log4aCNBO1.log             0        100 UNUSED
         4 /u02/database/CNBO1/redolog/log4bCNBO1.log             0        100 UNUSED

8 rows selected.

????4??С??

????a??????????????鵵??????ε????????????С????????????鵵??

????b???鵵??????????????????鵵??????????????????鵵?????????????????С?????

????c????????????????????仯??active??current????????????????

????d??active??current?????????д?????????????????crash recovery?????????????????

????e???л??????alter system switch logfile??????????????????仯??????????????checkpoint????