MULTIPLEXING REDOLOG FILES
- Redo log files are mainly used for recovering a database and also to ensure data commit.
- If a redo log file is lost, it will lead to data loss. To avoid this, we can maintain multiplexed copies of redo log files in different locations. These copies are together called as redo log group and individual files are called redo log members.
- Oracle recommends to maintain a min of 2 redo log groups with min of 2 members in each group.
- LGWR will write into members of same group parallely only if ASYNC I/O is enabled at OS level.
- Redo log files will have 3 states – CURRENT, ACTIVE and INACTIVE. Always these states will be changed in cyclic order.
- We cannot have different sizes for members in the same group, whereas we can have different sizes for different groups, but not recommended to implement.
- Default size of redo log member is 100mb in 9i and 50mb in 10g.
- In 8i, LOG_CHECKPOINT_INTERVAL parameter setting will specify the time at which checkpoint should occur where as from 9i the same can be achieved using FAST_START_MTTR_TARGET.
group by group#,members,status;
- Control file contains crucial database information and loss of this file will lead to loss of important data about database. So it is recommended to have multiplexed copies of files in different locations.
- If control file is lost in 9i, database may go for force shutdown, where as database will continue to run, if it is 10g version.