How to fix Error 3224 on Windows Server 2025 / Windows 11

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Microsoft SQL Server 2025 Troubleshooting Guide: Error 3224 – Cannot Create Worker Thread

Why This Error Happens

Error 3224 occurs when SQL Server is unable to allocate a new worker thread from the operating system to process backup, restore, or other I/O-intensive operations. This is typically caused by the server reaching its configured “max worker threads” limit, insufficient system memory/virtual address space, or OS-level thread pool exhaustion due to excessive concurrent connections. In some cases, this is also triggered by outdated SQL Server builds with known threading bugs on Windows Server 2025 or Windows 11, or by third-party antivirus/EDR software intercepting thread creation calls.

Step-by-Step Resolution Guide

Step 1: Check and Adjust Max Worker Threads Configuration

  • Open SQL Server Management Studio (SSMS) and connect to the instance via a Dedicated Administrator Connection (DAC) if the instance is unresponsive (Admin:ServerName).
  • Run EXEC sp_configure 'max worker threads'; to check the current value (0 = auto-configured, which is recommended for most workloads).
  • If manually set too low, reset it to auto with:
  EXEC sp_configure 'show advanced options', 1;
  RECONFIGURE;
  EXEC sp_configure 'max worker threads', 0;
  RECONFIGURE;
  • Restart the SQL Server service for changes to take effect.

Step 2: Verify System Memory and Virtual Address Space

  • Check Windows Task Manager or Performance Monitor (perfmon) for available physical memory and commit charge.
  • Ensure Max Server Memory in SQL Server is not set too high, starving the OS and other processes of RAM (navigate to SSMS → Server Properties → Memory).
  • On Windows Server 2025, confirm the server isn’t hitting the 2GB/4GB user-mode virtual address space limitation on 32-bit components (rare, but possible in mixed environments).
  • Increase physical RAM or adjust the SQL Server memory ceiling if the OS is memory-starved.

Step 3: Inspect SQL Server Error Log for Concurrent Session Spikes

  • Open the SQL Server Error Log via SSMS (Management → SQL Server Logs) or check the log file directly at:
    C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG
  • Look for patterns of connection spikes or runaway queries right before the 3224 error timestamp.
  • Use sys.dm_os_schedulers and sys.dm_exec_requests DMVs to identify if a specific application or job is exhausting the thread pool.
  • Kill or throttle the offending session/application using Resource Governor if identified.

Step 4: Update SQL Server 2025 Cumulative Updates

  • Check the currently installed build via SELECT @@VERSION;.
  • Download and apply the latest Cumulative Update (CU) from the Microsoft Update Catalog, as early 2025 builds have documented threading regressions on Windows 11/Server 2025 hosts.
  • Reboot the server after patching and confirm the service starts cleanly.

Step 5: Exclude SQL Server Processes from Antivirus/EDR Scanning

  • Add exclusions for sqlservr.exe, the data directory, and the log directory in Windows Defender or your third-party antivirus console.
  • Navigate to Windows Security → Virus & Threat Protection → Manage Settings → Add or Remove Exclusions.
  • Restart the SQL Server service and monitor whether thread creation errors persist.

Alternative or Verification Steps

  • To verify the fix, run a stress test using ostress or a simulated high-connection load, then check the Error Log for recurrence of Error 3224.
  • If the issue persists after all steps, consider migrating the instance to a server with increased core count/RAM, as the OS may be structurally incapable of supporting the configured workload’s thread demand.