Problem
When using a third-party backup tool to back up SAP HANA log segments, if the external storage system cannot be accessed, log backups will fail repeatedly. For example, access to an external storage system could be lost as a result of impacted network response times, an outage due to planned maintenance, or hardware failure.
In high-load scenarios, this can quickly cause the log area to grow until the file system is full. If, as a consequence, no more log segments can be created, this will cause SAP HANA to freeze.
Solution
You can enable log backup fallback to automatically detect downtimes in a third-party backup tool, and to temporarily redirect the writing of log backups to the file system. If the backup catalog is also configured to be backed up to the third-party storage system, backups of the backup catalog are also automatically redirected to the file system while log backup fallback is active.
To enable automatic log backup fallback, you need the SAP HANA system privilege DATABASE ADMIN. This can be configured by changing below parameter value to 'true' :
#Parameter change is online and no database restart is needed to affect.
log_backup_backint_fallback = trueBehavior
Controls whether log backups using backint will be automatically written to the filesystem, if backint is not available for several consecutive log backup attempts. A fallback to the filesystem is temporary as HANA will periodically attempt to perform log backups using backint again.
If a fallback is active and HANA finds backint to be available again the fallback ends. Otherwise, the fallback will remain in effect until the next attempt.
Note :
- A log backup fallback to the filesystem will also apply to catalog backups if catalog_using_backint=true.
- Requires log_backup_using_backint=true in order to take effect.Log Backup Fallback Location
If automatic log backup fallback is active, log backups are written to the path in the file system defined by the parameter basepath_logbackup. This path must be accessible by SAP HANA.
If the backup catalog is configured to be backed up to a third-party backup tool, if a fallback is active, backups of the backup catalog are written to the path in the file system defined by the parameter basepath_catalogbackup.
Identifying Which Log Backups Used Fallback
To check whether a log backup was written to the file system due to a fallback or not, refer to the monitoring view M_BACKUP_CATALOG_FILES. Column BACKINT_FALLBACK_USED has the following values:
FALSE : A log backup was written to the file system as configured.
TRUE : A log backup was originally configured to be written to a third-party backup tool, but was written to the file system due to an automatic log backup fallback.Log Backup Fallback is also Recorded
When a log backup fallback is triggered, alert 143 is raised. When the fallback is stopped, either automatically when log backups are being written again to the external storage system, or by disabling automatic log backup fallback, alert 143 is canceled.