Going Back to a Backup
Why-o-ever it may happen, databases can go corrupt. Be it a damaged file system, a system hang, or, Heaven forbid!, a DEVONthink crash. But, no reason to panic. First, run Tools > Verify & Repair. If DEVONthink cannot repair the database or if you are sure that you've lost some data, it's time for the internal backups. By default, DEVONthink keeps two internal backups of the database index files that you can revert to at any time.
Select Tools > Revert to Backup and choose one of the available backups. Then run Tools > Verify & Repair to make sure the backup is undamaged.
Note: DEVONthink never overwrites your current data with a backup but actually switches the current state of the database with the backup. So you can go also back to your most recent state at any time.