How to fix Error 3926 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3926

Why This Error Happens

Error 3926 occurs when a transaction is interrupted mid-process because another session forcibly committed or aborted it, typically during database restore, mirroring failover, or Always On Availability Group role transitions. This often happens when RESTORE operations run against a database while active transactions are still open in another session, or when a database snapshot/mirroring operation changes the database state unexpectedly. Corrupted transaction log entries or abrupt termination of a session using KILL can also trigger this inconsistency between the session’s transaction context and the actual database state.

Step-by-Step Resolution Guide

Step 1: Identify the Conflicting Session

  • Open SQL Server Management Studio (SSMS) and run sp_who2 or query sys.dm_exec_sessions to identify sessions interacting with the same database.
  • Check SQL Server Error Logs located at C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG for timestamps correlating with the error.
  • Look specifically for RESTORE DATABASE, ALTER DATABASE SET PARTNER, or mirroring/AG failover events near the error timestamp.

Step 2: Review and Isolate Long-Running Transactions

  • Run DBCC OPENTRAN('YourDatabaseName') to check for any uncommitted long-running transactions holding locks.
  • If a runaway transaction is found, safely terminate it using KILL <session_id> after confirming it is not critical.
  • Ensure application connection pooling is not reusing a session that was already committed/aborted by implementing proper TRY...CATCH and XACT_ABORT ON in your T-SQL scripts.

Step 3: Validate Always On / Mirroring Configuration

  • Open SQL Server Configuration Manager and verify the endpoint status for Always On Availability Groups under SQL Server Network Configuration.
  • In SSMS, navigate to Management > Always On High Availability and check the Dashboard for synchronization health.
  • If using Database Mirroring (legacy), confirm the witness server is reachable and not causing automatic failover mid-transaction.

Step 4: Rebuild the Transaction Log (If Corruption is Suspected)

  • Take a full backup of the database before proceeding: BACKUP DATABASE [YourDB] TO DISK = 'D:\Backups\YourDB.bak'.
  • Run DBCC CHECKDB('YourDatabaseName') WITH NO_INFOMSGS, ALL_ERRORMSGS to scan for log corruption.
  • If errors are found, use ALTER DATABASE [YourDB] SET EMERGENCY followed by DBCC CHECKDB repair options only as a last resort, since this can result in data loss.

Alternative or Verification Steps

  • Verify the fix by re-running the original failing transaction/query in a new session and confirming it completes with a COMMIT without triggering Error 3926.
  • If the issue persists, check Windows Event Viewer (Windows Logs > Application) on Windows Server 2025 for correlating MSSQLSERVER service restarts, which may indicate a deeper hardware or storage-level timeout causing the forced abort.