redo log日志组冗余

创建多个redo log日志组

说明：日志组根据需要来创建。而日志组的成员则需要至少2个，作为冗余策略。

SYS > alter database add logfile group 4 '/u01/app/oracle/data/db01/redo04.log' size 50m;

Database altered.

SYS > alter database add logfile member '/u01/app/oracle/data/db02/redo04.log' to group 4;

Database altered.

SYS > select * from v$log;

    GROUP#    THREAD#  SEQUENCE#      BYTES    MEMBERS ARC STATUS           FIRST_CHANGE# FIRST_TIME

---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ------------

         1          1        239   52428800          2 YES INACTIVE               2844284 21-JAN-10

         2          1        242   52428800          2 NO  CURRENT                2844297 21-JAN-10

         3          1        240   52428800          2 YES INACTIVE               2844291 21-JAN-10

         4          1        241   52428800          2 YES INACTIVE               2844293 21-JAN-10

SYS > select * from v$logfile;

    GROUP# STATUS  TYPE    MEMBER                         IS_

---------- ------- ------- ------------------------------ ---

         3         ONLINE  /u01/app/oracle/data/db01/redo NO

                           03.log

         2         ONLINE  /u01/app/oracle/data/db01/redo NO

                           02.log

         1         ONLINE  /u01/app/oracle/data/db01/redo NO

                           01.log

         4         ONLINE  /u01/app/oracle/data/db01/redo NO

                           04.log

    GROUP# STATUS  TYPE    MEMBER                         IS_

---------- ------- ------- ------------------------------ ---

         4         ONLINE  /u01/app/oracle/data/db02/redo NO

                           04.log

         2         ONLINE  /u01/app/oracle/data/db02/redo NO

                           02.log

         3         ONLINE  /u01/app/oracle/data/db02/redo NO

                           03.log

         1         ONLINE  /u01/app/oracle/data/db02/redo NO

    GROUP# STATUS  TYPE    MEMBER                         IS_

---------- ------- ------- ------------------------------ ---

                           01.log

SYS > alter system switch logfile;

System altered.

 SYS > alter system checkpoint;

System altered.