How to fix Error 3875 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 3875 – Internal Resource Pool Cannot Be Used for tempdb

Why This Error Happens

Error 3875 occurs when the SQL Server Resource Governor attempts to associate tempdb with a classifier function or workload group that routes it to a user-defined resource pool instead of the mandatory internal pool. Since tempdb is a shared system database used by all sessions and internal engine operations, SQL Server 2025 enforces that it can only operate under the internal resource pool to guarantee unrestricted access to memory and CPU scheduling. This conflict typically arises from a misconfigured classifier function, a corrupted Resource Governor configuration, or an improperly applied workload group policy pushed through a recent Group Policy or SQL Server configuration script on Windows Server 2025.

Step-by-Step Resolution Guide

Step 1: Verify Current Resource Governor Configuration

  • Open SQL Server Management Studio (SSMS) and connect via the Dedicated Admin Connection (DAC) using ADMIN:ServerName.
  • Run the following query to inspect pool assignments:
  SELECT * FROM sys.resource_governor_resource_pools;
  SELECT * FROM sys.resource_governor_workload_groups;
  • Confirm whether tempdb-related sessions are being misclassified into a non-internal pool.

Step 2: Disable or Correct the Classifier Function

  • Locate the custom classifier function under Databases > master > Programmability > Functions.
  • Temporarily disable it to isolate the issue:
  ALTER RESOURCE GOVERNOR WITH (CLASSIFIER_FUNCTION = NULL);
  ALTER RESOURCE GOVERNOR RECONFIGURE;
  • If a custom function is required, edit it to explicitly exclude system sessions (session_id <= 50) from being routed away from the internal pool.

Step 3: Reset Resource Governor to Default State

  • If corruption is suspected, fully disable Resource Governor:
  ALTER RESOURCE GOVERNOR DISABLE;
  • Restart the SQL Server service via services.msc or PowerShell:
  Restart-Service -Name 'MSSQLSERVER' -Force
  • Re-enable Resource Governor only after confirming tempdb initializes correctly under the internal pool.

Step 4: Check tempdb File Configuration and Permissions

  • Navigate to the tempdb data file path (commonly C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\).
  • Ensure the SQL Server service account has Full Control permissions on this directory.
  • Validate there are no orphaned or corrupted .mdf/.ldf files causing initialization conflicts with resource pool binding.

Alternative or Verification Steps

  • After applying fixes, run SELECT DB_NAME(database_id), * FROM sys.dm_exec_requests WHERE database_id = 2; to confirm tempdb sessions are now scheduled under the internal resource pool without errors.
  • If the error persists, perform a tempdb rebuild using SQL Server Configuration Manager by relocating the tempdb files to a new path and restarting the service, which forces a clean re-initialization of internal resource bindings.