Synchronizing databases using the transaction log – SQL Server Log shipping

No matter how well managed your systems are, accidents may still occur, and potentially lead to disastrous consequences. In order to ensure that there is a disaster recovery solution available, it is always good to have a standby copy of a primary database on another SQL Server instance.

The first way to achieve this is to utilize the SQL Server Log shipping.

SQL Server Log shipping allows you to automatically send transaction log backups from an original database located on a primary server instance to another database(s) on a different server instance(s). The transaction log backups need to be applied to each of the secondary databases individually.

How does this work:

  1. Backup of transaction log on the primary server instance is created
  2. Backup file is copied to another server instance
  3. Transaction log backup is restored on a second server instance

Prerequisites:

  • The primary database must use the full or bulk-logged recovery model (if a database recovery model is switched to simple, SQL Server log shipping will stop functioning)
  • Before you can configure log shipping in SQL Server, the transaction log backups must be made available to a secondary server by creating a share of the directory where the transaction log backups are generated into.

To configure the SQL Server log shipping:

  1. Navigate to a database you want to use as your primary database in SSMS object explorer, right click on it in and select Properties

  2. In the Select a page panel, click Transaction Log Shipping and check the Enable this as a primary database in a log shipping configuration check box

  3. Click Backup Settings
  4. In the Transaction Log Backup Settings dialog:
    • Specify the network path to the shared transaction log backup folder
    • If the backup folder is on the primary server, specify the local path to the backup folder in the If the backup folder is located on the primary server, type a local path to the folder field. If the backup folder is not on the primary server, this field should remain empty
    • Specify parameters for the Delete files older than and Alert if no backup occurs within options
    • Click on the Schedule button and customize parameters in the backup schedule, and provide name for the job in the Job name field
    • In the Set backup compression drop menu, select one of the compression settings: Use the default server setting, Compress backup, or Do not compress backup
  5. After all options in the Transaction Log Backup Settings dialog have been set, click the OK button to close the dialog

  6. Back in the Database properties dialog, in the Secondary server instances and databases dialog, click the Add button to bring up the Secondary Database Settings dialog, and do the following:
    1. Click Connect and connect to the instance of SQL Server that will be used as a secondary server
    2. In the Secondary Database field dialog, specify the name of the database that will be created, or choose existing database from the drop-menu list
    3. In the Initialize Secondary database, Copy files, and Restore tabs, choose the appropriate options/settings for the secondary database and click OK
  7. To monitor this log shipping configuration in SQL Server, the monitor server must be added at this point (it cannot be added later without replacing the whole configuration. Monitor server instance can be added by checking the Use a monitor server instance checkbox, and specifying server parameters in the Log shipping monitor settings dialog, accessed via the Settings button
  8. Click OK to finalize the process

This ensures that there is a copy of the primary database on other SQL Server instance which can be used as a safety precaution in case of a disaster, or used for any other purpose.

Even so, there are several cons to this method:

  • It is not possible to choose only part of the database, and exclude parts of the data from the transaction log
  • It is not possible to use SQL Server log shipping to a database with lower compatibility level, even when features of a newer level are not utilized
  • It is not possible to view the transactions that have occurred prior to shipping them, or after they’ve been applied

The second way to achieve this that will avoid the previously described cons is to use ApexSQL Log a SQL Server transaction log reader.

Ensuring that there is a standby copy of the primary database on other SQL Server instance can be achieved with ApexSQL Log by creating a Redo script which will replay the exact changes that have occurred:

  1. Start ApexSQL Log
  2. Connect to the SQL Server and choose the ‘original’ database from the database drop-list

  3. Click Next to advance
  4. The online transaction log for the selected database will be automatically selected. Add all transaction log backups to ensure that full chain of transaction log backups exists by clicking on the Add button and selecting appropriate backups from the Open dialog

    Selecting SQL logs to analyze

  5. In the next step of the wizard, choose the Undo/Redo option

  6. In the Filter setup feature specify time/date filters, Operations filters, Tables filters, or appropriate advanced options for your case. i.e. if a time between two synchronizations was one week, use the Custom filter to specify the time/date range


  7. In the Undo/Redo dialog, choose the Redo (Reconstruct) Script option

  8. Click Save batch script and specify the output path to create the .bat file containing the redo script
  9. The only remaining job is to automate this process. For this purpose, you can use the Windows Task Scheduler (Windows Scheduler). Here is a detailed solution on How to automate daily reports with ApexSQL Log

 

March 4, 2015