How to fix Error 1450 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 1450 — “ALTER DATABASE Failed Because the Worker Thread Cannot Be Created”

Why This Error Happens

This error typically occurs when SQL Server 2025 has exhausted its available worker thread pool, often due to the max worker threads configuration being set too low or the system experiencing memory pressure that prevents new threads from being allocated. It can also surface when the operating system itself is low on non-paged pool memory or when a large number of concurrent connections/requests are competing for the same thread resources during the ALTER DATABASE operation. In some cases, this is a symptom of thread starvation caused by blocking sessions or runaway queries that never release their worker threads back to the pool.

Step-by-Step Resolution Guide

Step 1: Check Current Worker Thread Configuration

  • Run sp_configure 'max worker threads' in SQL Server Management Studio (SSMS) to view the current value.
  • A value of 0 means SQL Server auto-configures threads based on CPU count; verify this hasn’t been manually overridden to a restrictively low number.
  • Cross-reference with sys.dm_os_sys_info by querying the max_workers_count column.

Step 2: Review System Resource Utilization

  • Open Task Manager or Performance Monitor (PerfMon) on Windows Server 2025 / Windows 11 and check for high CPU, memory, or handle usage tied to sqlservr.exe.
  • Check the Windows Event Viewer (Applications and Services Logs > MSSQLSERVER) for correlating out-of-memory or resource exhaustion warnings around the same timestamp as Error 1450.
  • Confirm available non-paged pool memory using PerfMon counter Memory > Pool Nonpaged Bytes; sustained high usage indicates OS-level thread starvation.

Step 3: Identify and Kill Blocking Sessions

  • Execute sp_who2 or query sys.dm_exec_requests to identify long-running or blocked sessions consuming worker threads unnecessarily.
  • Use SELECT * FROM sys.dm_os_waiting_tasks to pinpoint sessions stuck in a wait state (e.g., THREADPOOL wait type is a direct indicator of this issue).
  • Terminate problematic sessions using KILL <session_id> only after confirming they are not critical transactions.

Step 4: Increase Max Worker Threads or Restart the SQL Service

  • If thread count is manually capped too low, reset it to 0 (auto-configure) using:
  EXEC sp_configure 'max worker threads', 0;
  RECONFIGURE WITH OVERRIDE;
  • If the server is already under extreme load, perform a controlled restart of the SQL Server service via SQL Server Configuration Manager to clear the stuck thread pool.
  • Ensure the Windows Server 2025 host has sufficient physical RAM allocated to the SQL Server instance under Server Properties > Memory.

Step 5: Apply Latest Cumulative Update (CU)

  • Verify your SQL Server 2025 build number via SELECT @@VERSION and compare against the latest Cumulative Update from Microsoft’s official release notes.
  • Install any pending CU, as thread pool exhaustion bugs are frequently patched in maintenance releases.

Alternative or Verification Steps

  • After applying fixes, re-run the original ALTER DATABASE command during an off-peak window and confirm it completes without Error 1450.
  • As an alternative, monitor sys.dm_os_waiting_tasks for 15–20 minutes post-fix to ensure the THREADPOOL wait type no longer appears, confirming the thread starvation issue is resolved.