Wednesday, May 7, 2008

Sql Server Database Mirror and Recovery Model

When i've configured the Database Mirroring on my production environment, i've changed the database recovery model to full. Then, i've faced the issue with transaction log file size, that is increasing a lot, on all mirrored databases.

After some research, I found some information to solve this that i would like to share with you.

To prevent the transaction log files from growing unexpectedly, consider using one of the following methods:

• Set the size of the transaction log files to a large value to avoid the automatic expansion of the transaction log files.

• Configure the automatic expansion of transaction log files by using memory units instead of a percentage after you thoroughly evaluate the optimum memory size.
For additional information about the issues to consider when you configure the autogrow option, click the following article number to view the article in the Microsoft Knowledge Base:

315512 ( Considerations for autogrow and autoshrink configuration

• Change the recovery model. If a disaster or data corruption occurs, you must recover your database so that the data consistency and the transactional integrity of the database are maintained. Based on how critical the data in your database is, you can use one of the following recovery models to determine how your data is backed up and what your exposure to the data loss is:

•Simple recovery model

•Full recovery model

•Bulk-logged recovery model

By using the simple recovery model, you can recover your database to the most recent backup of your database. By using the full recovery model or the bulk-logged recovery model, you can recover your database to the point when the failure occurred by restoring your database with the transaction log file backups.
By default, in SQL Server 2000 and in SQL Server 2005, the recovery model for a SQL Server database is set to the Full recovery model. With the full recovery model, regular backups of the transaction log are used to prevent the transaction log file size from growing out of proportion to the database size. However, if the regular backups of the transaction log are not performed, the transaction log file grows to fill the disk, and you may not be able to perform any data modification operations on the SQL Server database.
You can change the recovery model from full to simple if you do not want to use the transaction log files during a disaster recovery operation.

• Back up the transaction log files regularly to delete the inactive transactions in your transaction log.

• Design the transactions to be small.

• Make sure that no uncommitted transactions continue to run for an indefinite time.

• Schedule the Update Statistics option to occur daily.

• To defragment the indexes to benefit the workload performance in your production environment, use the DBCC INDEXDEFRAG Transact-SQL statement instead of the DBCC DBREINDEX Transact-SQL statement. If you run the DBCC DBREINDEX statement, the transaction log may expand significantly when your SQL Server database is in Full recovery mode. Additionally, the DBCC INDEXDEGRAG statement does not hold the locks for a long time, unlike the DBCC DBREINDEX statement.
For additional information about defragmenting the indexes in SQL Server 2000, see the following Microsoft Web site: (

If you must run the DBCC DBREINDEX statement as a job that is a part of the database maintenance plan, you must break up the job into multiple jobs. Additionally, you must take the frequent backups for the transaction logs between the execution of the jobs.

You can see the full document on the following address.


KoryS said...

I thought Full Recovery model was REQUIRED for Database Mirroring...

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