Data Recovering from Current Online Redo Log Missing

A member of the group - or the entire group - of current online redo log files (that is, the redo log files in which the database changes are currently being recorded) is lost.

Use the entries in the ALERT file and in the LGWR trace file to analyze the error situation. You must check all sources of information for possible LGWR errors. Even if an error allows the instance to continue running (for example, at least one member of the current group can be written to, errors only in the other members), the error should be corrected as soon as possible.

If you have not been mirroring the online redo log files, as supported by Oracle (and have also not been using hardware-based mirroring), the risk of losing online redo log entries is significantly higher. To be able to perform a full recovery, only the entries from the current online redo log file are necessary. Use mirroring to guard against complete loss of the online redo log files. If the mirrored online redo log files are available, you can use these later to perform a complete recovery of the database. Otherwise you can only recover the database to the point of the missing redo log entries (that is, an incomplete recovery with loss of data).

For this reason, we strongly recommend once again that you make use of the Oracle options for mirroring the online redo log files.

Prerequisites

You must meet the following requirements:

• You used the Oracle option for mirroring the online redo log files (or have hardware-based mirroring), and therefore have at least one copy of each online redo log file (SAP default: two copies of the online redo log files).

• Apart from the one member of the current online redo log group, no other files have been damaged.

  If further files have been damaged, restore the missing files and the missing active redo log and follow the recovery procedure for the category of the missing file (control file or files of the system, user, or index tablespaces).

Procedure

1. If the database system is still active, use the SQLPLUS command shutdown abort to shut it down.

2. Determine the reason why the current online redo log files were lost by examining the ALERT and trace files.

3. Replace the missing online redo log files with a mirrored copy.

4. Start the database with the SQLPLUS command startup.

   The system automatically performs an instance recovery.

   Note

   If all members of the current redo log group have been lost, you can only perform an incomplete partial recovery. For more information, see the documentation on your Oracle database system or Performing Incomplete Recovery.