Wait Type HADR_DATABASE_WAIT_FOR_RESTART

Wait statistics, in the context of SQL Server, refer to the amount of time that a query spends waiting to access data in the database. When a client application requests data from the database, the request is placed in a queue and the client application must wait for its turn to access the data. The time that the query spends waiting is called a "wait" and is tracked by SQL Server. This information can be used to identify potential performance bottlenecks and optimize the performance of the database. Wait statistics are commonly used by database administrators to diagnose and troubleshoot performance issues in SQL Server.

In SQL Server Always On Availability Groups, certain wait types indicate specific operations related to high availability. One such wait type is HADR_DATABASE_WAIT_FOR_RESTART. Understanding this wait type can help you troubleshoot issues and maintain a smooth-running Always On environment.

What is HADR_DATABASE_WAIT_FOR_RESTART?

The HADR_DATABASE_WAIT_FOR_RESTART wait type occurs when SQL Server is waiting for a database in an Always On Availability Group to restart. This usually happens after a failover event, a recovery process, or during synchronization when a database needs to transition into a synchronized state.

In simpler terms, this wait indicates that SQL Server is holding off on certain operations until the database involved in the Always On setup has fully restarted and is ready for use. While this wait is expected during failovers or recovery events, prolonged waits can suggest underlying issues that need attention.

Why Does HADR_DATABASE_WAIT_FOR_RESTART Happen?

There are several reasons why this wait type might occur, including:

• A recent failover in the Always On Availability Group.
• Database recovery processes taking longer than expected.
• Resource constraints on the server hosting the restarting database, such as CPU or memory pressure.
• Network issues between the primary and secondary replicas, delaying synchronization.
• Large transaction logs or excessive recovery work required for the database.

Monitoring and addressing these issues can reduce the impact of HADR_DATABASE_WAIT_FOR_RESTART waits on your environment.

How to Monitor HADR_DATABASE_WAIT_FOR_RESTART Waits

To effectively track and analyze HADR_DATABASE_WAIT_FOR_RESTART waits, using a monitoring tool like Database Health Monitor is highly recommended. Its Historic Waits Monitoring feature provides detailed insights into when and why these waits occur, helping you identify patterns and correlate them with failovers, recovery events, or other system activities.

With Database Health Monitor, you can pinpoint issues related to database restarts and determine if delays are tied to server resource constraints or Always On configuration problems.

What Can You Do About HADR_DATABASE_WAIT_FOR_RESTART Waits?

If you’re encountering frequent or prolonged HADR_DATABASE_WAIT_FOR_RESTART waits, consider the following actions:

• Investigate the root cause of failover or recovery events to reduce their frequency.
• Optimize the Always On Availability Group configuration to improve failover and recovery times.
• Increase server resources, such as CPU or memory, to handle recovery operations more efficiently.
• Monitor and optimize transaction log size and recovery processes to reduce delays.
• Ensure that network connections between replicas are fast and reliable.

By addressing these areas, you can minimize HADR_DATABASE_WAIT_FOR_RESTART waits and ensure a faster return to normal operations after failovers or recovery events.

How Stedman Solutions Can Help

At Stedman Solutions, we specialize in SQL Server performance tuning and troubleshooting, including resolving issues with wait types like HADR_DATABASE_WAIT_FOR_RESTART. Our managed services offer proactive monitoring and expert guidance to optimize your Always On Availability Groups. Additionally, our Database Health Monitor is a powerful tool for tracking and analyzing SQL Server waits, ensuring your database environment performs at its best.

If your Always On setup is experiencing performance challenges or you want to optimize your SQL Server operations, contact us today. Let us help you achieve a reliable, high-performing SQL Server environment!

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Applies to

Related Waits

See Also

• More About HADR_DATABASE_WAIT_FOR_RESTART