History has shown us how civilizations thrived by utilizing efficient transportation methods. Just like cities that relied on rivers to transport lumber, SQL Server also has its own method of shipping logs. In this blog post, we will explore the concept of log shipping in SQL Server and discuss its importance in ensuring database availability and meeting SLAs.
Log shipping is a traditional high availability solution in SQL Server. As the name suggests, it involves shipping transaction log backups from one server to one or more servers. This process is based on the concept of transaction log backups, which can be taken from databases in full or bulk logged recovery models. In the simple recovery model, transaction log backups are not allowed due to the frequent flushing of the transaction log file.
When implementing log shipping, it is important to understand that all log backups form a chain. Each log backup must be restored in sequence, otherwise, an error message will be encountered during the restore process. The backup, copy, and restore operations are automatically performed by the SQL Agent service. The backup location is shared among the servers to allow other servers to obtain a copy of the log backup for restoration.
In log shipping, there are different server roles involved. The source server, also known as the primary server, is responsible for generating the log backups. The receiving servers are referred to as secondary servers. Additionally, there is a monitor server that checks the health of the copy, backup, and restore jobs. If any of these jobs are not running properly, the secondary servers may fall behind the primary server, compromising the high availability of the system.
Monitoring log shipping is crucial to ensure its effectiveness. SQL Server provides a Log Shipping Status report that allows administrators to view the status of log shipping. It is important to note that the data shown in the report depends on the server from which it is launched. If launched from the primary server, the report will display information about the backup section. On the other hand, if launched from a secondary server, the report will show information about the copy and restore operations.
The Log Shipping Status report can be further enhanced by configuring a monitor server. This allows administrators to view information about all three steps of log shipping (backup, copy, and restore). The report highlights any alarming issues in red, making it easier to identify delays or problems in the log shipping process.
To fetch the information displayed in the Log Shipping Status report, a simple query is executed behind the scenes: EXEC sp_help_log_shipping_monitor
. This query returns a result set containing status and other information for registered primary and secondary databases on a primary, secondary, or monitor server.
When encountering delays in log shipping, it is important to investigate the cause further. Common causes of delays can include networking issues, disk slowness, or other factors. Identifying and addressing these issues promptly is crucial to maintaining the high availability of the system.
In conclusion, log shipping is a valuable high availability solution in SQL Server. By understanding its concepts and monitoring its status, database administrators can ensure the availability of databases, meet SLAs, and address any issues that may arise. If you have any experiences or observations regarding log shipping delays, please share them in the comments below.