Wait Type PREEMPTIVE_COM_RELEASE

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 relies on different wait types to help identify where processes might be experiencing delays. One specific wait type, PREEMPTIVE_COM_RELEASE, appears when SQL Server is waiting for an external COM (Component Object Model) operation to release resources. This wait type can occur in environments where SQL Server interacts with external applications or systems through COM objects. In this post, we’ll explore what PREEMPTIVE_COM_RELEASE means, when it happens, and what it can tell us about SQL Server performance.

What Is the PREEMPTIVE_COM_RELEASE Wait Type?

The PREEMPTIVE_COM_RELEASE wait type happens when SQL Server is waiting for an external COM object to release resources. COM (Component Object Model) is a Microsoft technology that allows different applications and components to communicate with each other. SQL Server may use COM objects to interact with certain external applications or perform tasks like file manipulation, sending messages, or using OLE DB providers to connect to external data sources.

When SQL Server waits for a COM object to finish or release resources, it operates in “preemptive” mode, handing control over to the operating system. This is why it’s called a PREEMPTIVE_COM_RELEASE wait type – SQL Server is waiting for the operating system to finish handling the COM operation before it can continue with its own processing.

When Does PREEMPTIVE_COM_RELEASE Appear?

This wait type typically appears in environments where SQL Server interacts with external systems through COM components. Some common scenarios include:

• Linked Server Connections – When SQL Server connects to an external data source through linked servers using OLE DB providers, it may experience PREEMPTIVE_COM_RELEASE waits if these connections take time to complete.
• External Application Integration – SQL Server might use COM components to interact with other applications, such as sending emails, accessing the file system, or retrieving data from non-SQL databases.
• OLE Automation Procedures – If your SQL Server instance is using OLE Automation procedures, like sp_OACreate or sp_OAMethod, you may see PREEMPTIVE_COM_RELEASE waits as SQL Server waits for these external commands to complete.

While occasional PREEMPTIVE_COM_RELEASE waits are common when interacting with external systems, prolonged waits may indicate a performance issue with the external component or process.

Why PREEMPTIVE_COM_RELEASE Waits Matter

Some PREEMPTIVE_COM_RELEASE waits are normal in SQL Server environments that interact with external applications. However, frequent or long waits in this category can slow down SQL Server’s performance. If SQL Server frequently waits on external COM operations to release resources, it may affect the overall response time for other queries and processes.

Common causes of high PREEMPTIVE_COM_RELEASE waits include:

• Slow External Applications – If the external application or system that SQL Server is accessing is slow to respond, SQL Server may experience longer waits.
• Network Latency – For linked servers or external applications accessed over a network, high latency can increase wait times.
• Resource Constraints on External Systems – Limited resources, such as CPU or memory on the external system, can lead to longer wait times as SQL Server waits for the operation to complete.

How to Address PREEMPTIVE_COM_RELEASE Waits

If you are seeing frequent or prolonged PREEMPTIVE_COM_RELEASE waits, consider these strategies to help improve performance:

• Optimize Linked Server Performance – Try to minimize linked server calls or optimize linked server queries to reduce dependency on external data sources.
• Review Network Latency – If external systems are accessed over a network, check network performance to ensure low latency and reliable connections.
• Optimize External Applications – Make sure the external applications or COM objects that SQL Server relies on have sufficient resources and are optimized for performance.
• Limit OLE Automation Procedures – If possible, avoid OLE Automation stored procedures within SQL Server as they can lead to dependency on external components, increasing wait times.

Conclusion

The PREEMPTIVE_COM_RELEASE wait type in SQL Server indicates that SQL Server is waiting for an external COM object to release resources. While this wait type is common in environments that integrate with external applications, prolonged or frequent waits could signal issues with external performance or network latency. By optimizing linked server usage, reviewing network performance, and ensuring that external systems are running smoothly, you can help reduce PREEMPTIVE_COM_RELEASE waits and improve SQL Server efficiency.

For expert assistance in SQL Server performance tuning and optimizing external system integrations, Stedman Solutions offers managed services to help keep your SQL Server environment running at its best.

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Applies to

• SQL Server 2016
• SQL Server 2017
• SQL Server 2019
• SQL Server 2022

Related Waits

See Also

• More About PREEMPTIVE_COM_RELEASE