Synthetic full backup is a method for combining incremental backup into a full backup. It is not a new thing, many backup utilities can do that with file system backups. It is also well described:
However, there is only one backup suite that can do that with Oracle RDBMS: Commvault 11.
How is it done? Well, Commvault is a very well documented tool, the documentation is here:
To perform a synthetic full backup, Commvault will use storage snapshot to snap LUN(s) on which database lives, then use their proprietary block level backup to backup the snapshot to designated backup storage and then combine the incremental backup with the previous backup, to produce a “synthetic full backup”. Why is that a big deal which deserves a blog post? I am notoriously lazy when it comes to blogging and do not post very often. However, this is a big deal. The reason why this is a big deal is that this backup method eliminates regular full backups. A full backup needs to be taken only once, as the baseline. All subsequent backups are only incremental. And that means fast.
This helps with multi TB data warehouses which contain huge amounts of data, but are only loaded every few days, with few GB of information. Incremental backup will be a few GB in size and will be combined with the previous backups to form a “synthetic full”. Synthetic full backup contains only the data blocks, not archive logs. Once it is restored, the log files will still need to be applied. It can be used to restore either the entire database or just a part of it. I was lucky enough to test it and it works really well.
The backups are NOT combined on the database server, so the database users will not suffer. Backups are combined on another computer which is known as “media agent” in Commvault vernacular. For all the gory details, please contact your friendly neighbourhood Commvault sales office.