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Win32Exception ExecuteDbDataReaderAsync #4094

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Win32Exception ExecuteDbDataReaderAsync#4094
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paulmedynski
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Area\AsyncPerformance 📈Issues that are targeted to performance improvements.

Description

@bmahouachi
bmahouachi
opened on Mar 26, 2026

During a higher load on the API, several Win32Exception are raised that are not due to the database.

**Exception message:**
Microsoft.Data.SqlClient.SqlException (0x80131904): Execution Timeout Expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
 ---> System.ComponentModel.Win32Exception (258): Unknown error 258
   at Microsoft.Data.SqlClient.SqlCommand.EndExecuteReaderAsync(IAsyncResult asyncResult)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
ClientConnectionId:6076c28d-cfa1-456a-9749-b293d75316d8
Error Number:-2,State:0,Class:11
**Stack trace:**
Microsoft.Data.SqlClient.SqlException:
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Threading.ExecutionContext.RunInternal (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Threading.ExecutionContext.RunInternal (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Dapper.SqlMapper+<QueryRowAsync>d__34`1.MoveNext (Dapper, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null: /_/Dapper/SqlMapper.Async.cs:489)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at XX.XX.XX.XX.Infrastructure.XXRepository+<SubmitXXAsync>d__11.MoveNext (XX.XX.XX.XX.Infrastructure, Version=2.2.0.0, Culture=neutral, PublicKeyToken=null: F:\agent01\_work\17\s\src\Core\src\XX.Infrastructure\XXRepository.cs:73)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at XX.XX.XX.XX.Infrastructure.XXRepository+<SubmitXXAsync>d__13.MoveNext (XX.XX.XX.XX.Infrastructure, Version=2.2.0.0, Culture=neutral, PublicKeyToken=null: F:\agent01\_work\17\s\src\Core\src\XX.Infrastructure\XXRepository.cs:103)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at XX.XX.XX.XX.Services.Commands.XX.SubmitXXCommandHandler+<Handle>d__8.MoveNext (XX.XX.XX.XX.Services.Commands, Version=2.2.0.0, Culture=neutral, PublicKeyToken=null: F:\agent01\_work\17\s\src\Core\src\XX.Services.Commands\XX\XXXCommandHandler.cs:142)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at XX.XX.XX.XX.WebApp.Controllers.XXController+<CreateXX>d__9.MoveNext (XX.XX.XX.XX.Api, Version=2.2.0.0, Culture=neutral, PublicKeyToken=null: F:\agent01\_work\17\s\src\Core\src\XX.Api\Controllers\XXController.cs:183)
Inner exception System.ComponentModel.Win32Exception handled at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke:

Further technical details

The stored procedure response time:

Image

Microsoft.Data.SqlClient version: 6.1.4
.NET target: .NET 8.0
SQL Server version: Azure SQL server
Operating system: Azure linux app service

Additional context
Actions that we have made trying to fix:

Upgrades:
Dapper: from 2.0.123 to 2.1.35
Microsoft.Data.SqlClient: from 5.1.0 to 6.1.4

Infrastructure scale-out: from 8 instances to 12 instances

Min threads:
When analyzing the memory dump:
Image

We decided to set the minthread:
ThreadPool.SetMinThreads(workerThreads: 100, completionPortThreads: 100);

After setting the minthread to 100 it seems to be fixed. But we think that it's not the right fix to do because the lib is doing sync over async which is causing a thread starvation situation and the fix has to be done there. What do you think?

Activity

  1. github-project-automation
    moved this to To triage in SqlClient Boardon Mar 26, 2026
  2. github-project-automation
    added this to SqlClient Boardon Mar 26, 2026
  3. cheenamalhotra
    added the
    Bug
    issue type on Mar 28, 2026
  4. cheenamalhotra
    added
    Performance 📈Issues that are targeted to performance improvements.
    on Mar 28, 2026

  5. cheenamalhotra commented on Mar 28, 2026

    @cheenamalhotra
    cheenamalhotra
    on Mar 28, 2026
    Member

    Hi @bmahouachi

    Related to #422 and #1530.

  6. cheenamalhotra
    assigned
    paulmedynski
    on Mar 28, 2026
  7. cheenamalhotra
    moved this from To triage to Backlog in SqlClient Boardon Mar 28, 2026
  8. mdaigle
    added a parent issue on Apr 1, 2026
  9. mdaigle
    removed a parent issue on Apr 1, 2026
  10. mdaigle
    added a parent issue on Apr 1, 2026
  11. cheenamalhotra
    added
    Area\Async
    Performance 📈Issues that are targeted to performance improvements.
    and removed
    Performance 📈Issues that are targeted to performance improvements.
    on Jun 10, 2026

  12. priyankatiwari08 commented on Sep 17, 2026

    @priyankatiwari08
    priyankatiwari08
    on Sep 17, 2026
    Contributor

    /triage

  13. github-actions commented on Sep 17, 2026

    @github-actions
    github-actionsbot
    on Sep 17, 2026 – with GitHub Actions

    🔍 Triage Summary (on-demand re-triage)

    Check Result
    Issue type Bug
    Environment All required environment details provided for investigation
    Area Area\Async
    Duplicates Potentially related: #422, #1530 (parent, already linked by maintainer)
    Regression Not indicated — issue persisted after upgrading Microsoft.Data.SqlClient from 5.1.0 to 6.1.4, so this is not a new regression but a pre-existing behavior

    Analysis

    Under sustained load, SqlCommand.EndExecuteReaderAsync surfaces a Win32Exception (258) wrapped inside a SqlException "Execution Timeout Expired" that is not caused by the database itself. The reporter's own investigation (thread-pool dump analysis, and the fact that manually raising ThreadPool.SetMinThreads mitigates the symptom) strongly points to thread-pool starvation from sync-over-async code paths inside the async command-execution internals rather than an actual server-side timeout. This matches the pattern already tracked in the parent issue #1530 and related issue #422. Severity: P2 (has a viable workaround via increasing min threads, but indicates an underlying inefficiency in the async execution path affecting scalability under load).

    Next Steps

    • Recommend reviewing Queries with MultipleActiveResultSets=True (MARS) are very slow / time out on Linux #422 and Intermittent Unknown error 258 with no obvious cause #1530 for prior analysis/context before further investigation, since this looks like the same underlying thread-starvation pattern.
    • Assign to Copilot coding agent to investigate the async execution path in SqlCommand (EndExecuteReaderAsync and the underlying TdsParser/network-read continuations) for any remaining sync-over-async or blocking calls that could starve the thread pool under concurrent load, particularly around timeout handling in the async reader completion path.
    • Ask the reporter (@bmahouachi) if they can share a minimal reproducible load-test sample, as a concrete repro would help confirm whether the root cause is in SqlClient's async internals or an interaction with Dapper's async wrapper.

    Note: This triage summary is auto-generated by an AI agent. The analysis and suggestions above have not been verified by a human maintainer. Please treat as preliminary guidance only.

    Generated by SqlClient Issue Auto-Triage for #4094 · copilot · auto · 47.6 AIC · ⌖ 13 AIC · ⊞ 11.9K · ◷

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