Recovery Models

Full recovery Model

The "Full" recovery model tells SQL Server to keep all transaction data in the transaction log until either a transaction log backup occurs or the transaction log is truncated. The way this works is that all transactions that are issued against SQL Server first get entered into the transaction log and then the data is written to the appropriate data file.  This allows SQL Server to rollback each step of the process in case there was an error or the transaction was cancelled for some reason.  So when the database is set to the "Full" recovery model since all transactions have been saved you have the ability to do point in time recovery which means you can recover to a point right before a transaction occurred like an accidental deletion of all data from a table.

The full recovery model is the most complete recovery model and allows you to recover all of your data to any point in time as long as all backup files are useable. With this model all operations are fully logged which means that you can recover your database to any point. In addition, if the database is set to the full recovery model you need to also issue transaction log backups otherwise your database transaction log will continue to grow forever.

Here are some reasons why you may choose this recovery model:

• Data is critical and data can not be lost.
• You always need the ability to do a point-in-time recovery.
• You are using database mirroring

Type of backups you can run when the data is in the "Full" recovery model:

• Complete backups
• Differential backups
• File and/or Filegroup backups
• Partial backups
• Copy-Only backups
• Transaction log backups

ALTER DATABASE AdventureWorks SET RECOVERY FULL
GO

Simple recovery model

The "Simple" recovery model does what it implies, it gives you a simple backup that can be used to replace your entire database in the event of a failure or if you have the need to restore your database to another server.  With this recovery model you have the ability to do complete backups (an entire copy) or differential backups (any changes since the last complete backup).  With this recovery model you are exposed to any failures since the last backup completed.  

The "Simple" recovery model is the most basic recovery model for SQL Server.  Every transaction is still written to the transaction log, but once the transaction is complete and the data has been written to the data file the space that was used in the transaction log file is now re-usable by new transactions.  Since this space is reused there is not the ability to do a point in time recovery, therefore the most recent restore point will either be the complete backup or the latest differential backup that was completed.  Also, since the space in the transaction log can be reused, the transaction log will not grow forever as was mentioned in the "Full" recovery model.

Here are some reasons why you may choose this recovery model:

• Your data is not critical and can easily be recreated
• The database is only used for test or development
• Data is static and does not change
• Losing any or all transactions since the last backup is not a problem
• Data is derived and can easily be recreated

Type of backups you can run when the data is in the "Simple" recovery model:

• Complete backups
• Differential backups
• File and/or Filegroup backups
• Partial backups
• Copy-Only backups

ALTER DATABASE AdventureWorks SET RECOVERY SIMPLE

Bulk-logged recovery model

The "Bulk-logged" recovery model sort of does what it implies.  With this model there are certain bulk operations such as BULK INSERT, CREATE INDEX, SELECT INTO, etc... that are not fully logged in the transaction log. The advantage of using the "Bulk-logged" recovery model is that your transaction logs will not get that large if you are doing bulk operations and it still allows you to do point in time recovery as long as your last transaction log backup does not include a bulk operation as mentioned above.  If no bulk operations are run, this recovery model works the same as the Full recovery model.  One thing to note is that if you use this recovery model you also need to issue transaction log backups otherwise your database transaction log will continue to grow.

Here are some reasons why you may choose this recovery model:

• Data is critical, but you do not want to log large bulk operations
• Bulk operations are done at different times versus normal processing.
• You still want to be able to recover to a point in time

Type of backups you can run when the data is in the "Bulk-logged" recovery model:

• Complete backups
• Differential backups
• File and/or Filegroup backups
• Partial backups
• Copy-Only backups
• Transaction log backups

ALTER DATABASE AdventureWorks SET RECOVERY BULK_LOGGED