In addition to backing up the transaction log, a backup operation can rename the online transaction log to a file name of the form YYMMDDxx.log. This file is no longer used by the database server, but is available for the Message Agent. It is called an offline transaction log. A new online transaction log is started with the same name as the old online transaction log.
The YYMMDDxx.log file names are used to distinguish between the files, not for ordering. For example, the renamed log file from the first backup on December 10, 2000, is named 001210AA.log. The first two digits indicate the year, the second two digits indicate the month, the third two digits indicate the day of the month, and the final two characters distinguish among different backups made on the same day.
The Message Agent can use the offline copies to provide the old transactions as needed. If you set the delete_old_logs database option to On, then the Message Agent deletes the offline files when they are no longer needed, saving disk space.
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