A member of the group - or the entire group - of current online redo log files (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. Also use the SAPDBA Check function (Check (and repair) database ® Check database). It is the database administrator’s responsibility to check all sources of information for possible LGWR errors. Even if an error allows the instance to continue running (e.g. 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. In order 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 will only be able to recover the database to the point of the missing redo log entries (i.e. a partial 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.
Recovery Procedure: Mirrored Current Redo Log Files
For this recovery procedure, we assume that the following requirements are met:
- 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: one copy 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).
Proceed with the recovery as follows:
- If the database system is still active, use the SVRMGR command shutdown abort to shut it down.
- Determine the reason why the current online redo log files were lost. Examine the ALERT and trace files.
- Replace the missing online redo log files with one of their mirrored copies.
- Start the database with the SVRMGR command startup. The system automatically performs an instance recovery.
If all members of the current redo log group have been lost, you can only perform a partial recovery. For more information, please refer to the documentation on your ORACLE database system or the section Partial Recovery.
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