Handle Online redo log errors

1: How redo log works:

Online redo logs store a record of transactions that have occurred in your database. online redo logs exist solely to provide a mechanic for you to recover your database in the event of a failure. you are required to have at least two online redo log groups in your database. each online redo log group must contain at least one online redo log member. the member is the physical file that exists on disk. you can create multiple members in each redo log group, which is known as multiplexing your online redo log group.

NOTE: Online redo logs record all changes in the database. Online redo logs are processed cyclically.

2: how to minimize the data loss caused by redo errors:

• Multiplex groups to have multiple members.

• Never allow two members of the same group to share the same controller.
• Never put two members of the same group on the same physical disk.
• Ensure operating system file permissions are set appropriately.
• Use physical storage devices that are redundant (that is, RAID ).
• Appropriately size the log files so that they switch and are archived at regular intervals.
• Set the archive_lag_targetinitialization parameter to ensure that the online redo logs

Are switched at regular intervals

 

3: Determining How to Restore

 

• Inspect the alert. log file to determine which online redo log files have experienced a media failure.
• Query V $ LOG and V $ LOGFILE to determine the status of the log group and degree of multiplexing.
• If there is still one functioning member of a multiplexed group, fix the remaining failed member (s ).
• Depending on the status of the log group

Select. group #,. thread #,. status, B. member, B. status from v $ log a, v $ logfile B where. group # = B. group # order by. group #, B. group #;

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