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After the latest SQL Server 2019 CU, KB5037331, I receive the following message repeatedly in a couple of my SqlServer Server logs: "Long asynchronous API Call: The scheduling fairness of scheduler can be impacted by an asynchronous API invocation unexpectedly exceeding [large 8 digit number] ms."

I saw in the update notes the following change:

"Adds the following log message when high I/O latencies are detected in Bufferpool Lazy Writer (ntdll!ZwWriteFile system call) due to a performance issue in the underlying storage:

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

The problem is I don't know what I'm supposed to do with that information beyond basic I/O troubleshooting. What do I need to kill to make this message stop? And how do I identify what files/objects are involved in the I/O issue to solve the underlying problem?

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2 Answers 2

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MSFT has added it as a feature which moreover is an issue now. They are well aware of this and will most likely fix this in next CU as mentioned in their website

"Known issues in this update Issue one: Excessive logging of asynchronous API call warning in the error log The newly-created warning message in issue 2901635 might fill up the SQL Server error log with thousands of occurrences. The message is "WARNING Long asynchronous API Call: The scheduling fairness of scheduler can be impacted by an asynchronous API invocation unexpectedly exceeding xxx ms." This is due to an incorrect code change during the build process. Microsoft is working on a fix for this issue and it will be available in a future CU."

https://learn.microsoft.com/en-us/troubleshoot/sql/releases/sqlserver-2019/cumulativeupdate27#known-issues-in-this-update

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  • Ah ok, I think that's what the other commenter was trying to bring to my attention. Must have skimmed too fast and went right past the section about the known issue with that update.
    – Jeff Bauersfeld
    Commented Jul 12 at 2:51
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This is a known issue with the Patch CU27.

See: https://learn.microsoft.com/en-us/troubleshoot/sql/releases/sqlserver-2019/cumulativeupdate27#2901635

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  • Yeah, that's where I got the explanatory text from in the OP. But it's listed as a feature, so calling it a "known issue" is probably a misnomer. I just don't know what to do with that info.
    – Jeff Bauersfeld
    Commented Jun 30 at 22:04

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