Wait Type CLR_AUTO_EVENT

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 uses various wait types to identify where delays may occur during processing. The CLR_AUTO_EVENT wait type is related to the Common Language Runtime (CLR), which allows SQL Server to execute .NET Framework code. This wait type occurs when a thread using CLR is waiting on an automatic event to be signaled. Understanding this wait type is essential for troubleshooting performance issues involving CLR integration.

What Is the CLR_AUTO_EVENT Wait Type?

The CLR_AUTO_EVENT wait type appears when SQL Server’s CLR thread is waiting on an automatic event, which acts as a synchronization mechanism between threads. This wait type typically signals that CLR-based code or processes are encountering delays, potentially due to resource contention, configuration issues, or inefficiencies in the .NET code being executed.

When Does CLR_AUTO_EVENT Appear?

This wait type commonly occurs in the following scenarios:

• CLR Integration – When SQL Server is executing user-defined CLR functions, stored procedures, or triggers written in .NET.
• Thread Synchronization – When CLR threads are waiting for another thread to release a resource or signal an event.
• High Concurrency – In systems with many CLR tasks running simultaneously, leading to potential contention or synchronization delays.
• Resource Constraints – When CPU, memory, or other resources are insufficient to handle the CLR workload efficiently.

Why CLR_AUTO_EVENT Waits Matter

While some CLR_AUTO_EVENT waits are expected in systems leveraging CLR integration, excessive or prolonged waits can indicate performance issues. Common causes include:

• Inefficient CLR Code – Poorly optimized .NET code can take longer to execute, increasing wait times.
• Thread Contention – High concurrency or inadequate synchronization logic can cause threads to wait unnecessarily.
• Resource Bottlenecks – Limited CPU or memory availability can delay CLR operations.
• Configuration Issues – Misconfigured CLR settings or excessive task queuing can impact performance.

How to Address CLR_AUTO_EVENT Waits

If this wait type is impacting your system’s performance, consider the following strategies:

• Optimize CLR Code – Review and refine the .NET code being executed to ensure it is efficient and well-written.
• Reduce CLR Dependence – Where possible, replace CLR-based logic with native T-SQL to reduce reliance on CLR.
• Monitor Thread Contention – Use performance monitoring tools to identify and address synchronization bottlenecks in CLR tasks.
• Allocate Resources – Ensure the server has sufficient CPU and memory to handle the CLR workload effectively.
• Validate CLR Configuration – Check SQL Server’s CLR settings and adjust them based on your workload’s needs.

Monitoring CLR_AUTO_EVENT Waits

To effectively monitor this wait type, use the Historic Waits Monitoring feature in Database Health Monitor. This tool tracks wait statistics over time, helping you identify patterns and diagnose CLR-related bottlenecks. By monitoring waits regularly, you can proactively address performance issues and maintain system stability.

Stedman Solutions specializes in SQL Server performance tuning and optimization. Whether you’re dealing with CLR_AUTO_EVENT waits or other SQL Server challenges, our Database Health Monitor provides valuable insights, and our managed services deliver expert support to keep your SQL Server environment running efficiently. 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_AUTO_EVENT