How to fix Error 3868 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 3868 – Failed to Start tempdb Metadata Memory-Optimized Mode

Why This Error Happens

This error occurs when SQL Server 2025 attempts to initialize tempdb in memory-optimized metadata mode but fails due to insufficient memory allocation, a corrupted or locked model/tempdb system file, or inadequate permissions on the SQL Server service account to access the configured data directories. It can also happen if the server was abruptly restarted or crashed during a previous attempt to enable this feature, leaving the configuration in a partially applied state. SQL Server gracefully falls back to standard SQL-based tempdb startup to keep the instance available, but the memory-optimized configuration must be manually re-applied.

Step-by-Step Resolution Guide

Step 1: Verify SQL Server Service Account Permissions

  • Open Services.msc on Windows Server 2025 / Windows 11 and confirm the account running the “SQL Server (MSSQLSERVER)” service.
  • Ensure this account has Full Control on the tempdb data/log file directories (typically C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA).
  • Right-click the folder, go to Properties > Security, and add the service account if missing.

Step 2: Check Available System Memory and Resource Governor Settings

  • Memory-optimized tempdb metadata requires sufficient free memory at startup; confirm the server has adequate RAM headroom (at least 2–4 GB free beyond SQL Server’s max memory cap).
  • Run the following query to check current memory configuration:
EXEC sp_configure 'max server memory';
  • If memory is constrained, lower max server memory (MB) via sp_configure and restart the SQL Server service to free up room for tempdb initialization.

Step 3: Re-run the ALTER SERVER CONFIGURATION Command

  • Open a new query window in SQL Server Management Studio (SSMS) connected via a Dedicated Admin Connection (DAC) if the instance is unstable.
  • Execute the command again exactly as prompted:
ALTER SERVER CONFIGURATION SET TEMPDB METADATA = MEMORY_OPTIMIZED;
  • Restart the SQL Server service through SQL Server Configuration Manager (not just via Services.msc) to ensure startup parameters reload correctly.

Step 4: Inspect the SQL Server Error Log for Underlying Failures

  • Navigate to C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG.
  • Search for entries immediately preceding Error 3868, such as “Could not allocate space” or “Access is denied,” which indicate the specific blocking cause.
  • Resolve any referenced file-lock or disk-space issues (ensure at least 10% free space on the tempdb volume) before retrying Step 3.

Step 5: Rebuild tempdb Configuration via Startup Parameters (If Repeated Failures Persist)

  • Open SQL Server Configuration Manager > SQL Server Services, right-click the instance, and select Properties > Startup Parameters.
  • Temporarily remove any custom trace flags related to tempdb (e.g., -T174 or similar) that may conflict with memory-optimized initialization.
  • Restart the service and re-attempt the ALTER SERVER CONFIGURATION command from Step 3.

Alternative or Verification Steps

  • Verify success by running SELECT SERVERPROPERTY('IsTempdbMetadataMemoryOptimized'); — a return value of 1 confirms the feature is active.
  • If the issue persists after multiple attempts, disable the feature entirely with ALTER SERVER CONFIGURATION SET TEMPDB METADATA = NON_MEMORY_OPTIMIZED; and restart, then re-enable it only after confirming memory and disk prerequisites are fully met.