SQL Server 2019 CU 27 Bug: “WARNING Long asynchronous API Call” Error Log Flooding

Introduction

With the release of SQL Server 2019 CU 27, some users have encountered a bug that causes the error log to be flooded with the following warning message:

WARNING Long asynchronous API Call: The scheduling fairness of scheduler can be impacted by an asynchronous API invocation unexpectedly exceeding xxx ms.

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This issue results from an incorrect code change during the build process of CU 27. If you experience this issue and prefer not to uninstall the CU, there are several steps you can take to resolve it.

Understanding the Issue

The warning message indicates that an asynchronous API call is taking longer than expected, which can impact the scheduling fairness of the scheduler. While this doesn’t necessarily indicate a critical failure, the continuous logging of these warnings can overwhelm your error log, making it difficult to identify other important messages.

Workarounds and Solutions

1. Move to a Newer Version

One of the most effective solutions is to upgrade to a newer cumulative update (CU) that addresses this issue. Microsoft typically resolves such bugs in subsequent updates. Check the latest CU releases for SQL Server 2019 and upgrade to a version where this issue has been fixed.

2. Revert to an Older Version

If upgrading to a newer version is not immediately feasible, you can revert to an older CU version where this issue was not present. While this might not always be ideal, it can serve as a temporary workaround until a more permanent solution is implemented.

3. Contact Microsoft Support

For those who prefer not to downgrade or cannot upgrade immediately, contacting Microsoft Support is a viable option. Microsoft Support can provide guidance and potentially offer a hotfix or workaround tailored to your specific environment.

Steps to Contact Microsoft Support

1. Visit the Microsoft Support website.
2. Navigate to the SQL Server support section.
3. Provide details about your issue, including the error message and context.
4. Follow the instructions given by the support team to implement any provided solutions or workarounds.

Preventive Measures

To avoid similar issues in the future, consider the following best practices:

• Regularly Backup Databases: Ensure that you have recent backups before applying any cumulative updates.
• Test Updates in a Staging Environment: Before applying CUs to your production environment, test them in a staging environment to identify potential issues.
• Stay Informed: Keep an eye on SQL Server release notes and community forums for any reported issues with new updates.

Conclusion

The “WARNING Long asynchronous API Call” error log flooding in SQL Server 2019 CU 27 can be addressed by moving to a newer or older version, or by contacting Microsoft Support for assistance. While this bug is an inconvenience, it underscores the importance of cautious update management and the value of having a robust support system in place.

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