Wait Type CLR_MONITOR

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.

SQL Server tracks a wide variety of wait types to help identify where delays occur in its operations. The CLR_MONITOR wait type is associated with the Common Language Runtime (CLR), which allows SQL Server to execute .NET code. This wait type appears when SQL Server is waiting for a CLR-related synchronization mechanism. Understanding this wait type can help diagnose issues related to CLR integration and ensure smooth performance.

What Is the CLR_MONITOR Wait Type?

The CLR_MONITOR wait type occurs when a SQL Server thread is waiting on a monitor, a synchronization construct used in CLR for thread coordination. It is often seen in environments where user-defined CLR code, such as functions, procedures, or triggers, is in use. This wait type signifies that a thread is waiting for another thread to release the monitor so it can proceed.

When Does CLR_MONITOR Appear?

This wait type typically appears in the following scenarios:

• CLR Code Execution – When SQL Server is running CLR-based code and threads are competing for access to a synchronized resource.
• High Concurrency – In systems with many CLR tasks running simultaneously, leading to thread contention.
• Inefficient CLR Logic – Poorly written .NET code that excessively locks resources or performs long-running tasks within monitors.
• Resource Bottlenecks – When server resources like CPU or memory are limited, it can exacerbate CLR thread synchronization delays.

Why CLR_MONITOR Waits Matter

While CLR_MONITOR waits are expected in systems utilizing CLR integration, prolonged or frequent waits can indicate potential issues. Common causes include:

• Thread Contention – High concurrency in CLR operations can lead to multiple threads waiting for shared resources.
• Inefficient Code – Poorly optimized CLR logic that frequently locks resources can increase wait times.
• Limited Server Resources – Insufficient CPU or memory to handle CLR tasks efficiently.
• Excessive CLR Usage – Over-reliance on CLR-based operations instead of native T-SQL can lead to synchronization issues.

How to Address CLR_MONITOR Waits

If CLR_MONITOR waits are affecting your SQL Server performance, consider these strategies:

• Review CLR Code – Analyze and optimize the .NET code being executed to minimize locking and synchronization overhead.
• Reduce CLR Usage – Replace CLR-based logic with native T-SQL where possible to reduce dependency on CLR operations.
• Improve Resource Allocation – Ensure the server has sufficient CPU and memory to handle the CLR workload effectively.
• Monitor Concurrency – Identify and address contention issues by balancing the load across threads and resources.
• Enable CLR Profiling – Use tools like SQL Server Profiler or Extended Events to identify inefficient CLR routines and optimize them.

Monitoring CLR_MONITOR Waits

To track this wait type effectively and identify its impact over time, use the Historic Waits Monitoring feature in Database Health Monitor. This tool provides detailed insights into wait statistics, helping you spot trends, diagnose bottlenecks, and optimize CLR performance. Regular monitoring ensures that your SQL Server runs smoothly and efficiently.

Stedman Solutions specializes in SQL Server performance tuning and troubleshooting. Whether you’re experiencing CLR_MONITOR waits or other performance challenges, our Database Health Monitor provides powerful insights, and our managed services deliver expert support to keep your SQL Server environment running at its best. Contact us today to learn how we can help improve your SQL Server performance and reliability.

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Applies to

Related Waits

See Also

• More About CLR_MONITOR