How to fix Error 4312 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4312 – Log Chain Gap Detected

Why This Error Happens

This error occurs when SQL Server detects a discontinuity in the transaction log sequence, typically caused by a missing differential or transaction log backup between the last full backup and the log you’re attempting to restore. It can also happen if a database was switched from SIMPLE to FULL recovery model without taking a new full backup afterward, which resets the log chain. Additionally, an intervening backup taken by another tool or process (such as a third-party agent) that truncated the log without your knowledge can silently break the chain.

Step-by-Step Resolution Guide

Step 1: Verify the Current Log Chain Status

  • Run the following query against the msdb database to review backup history:
  • SELECT database_name, backup_start_date, type, is_copy_only FROM msdb.dbo.backupset WHERE database_name = 'YourDBName' ORDER BY backup_start_date;
  • Look for type = 'D' (full), 'I' (differential), and 'L' (log) entries to identify where the gap begins.
  • Confirm the last_lsn of your most recent restored backup matches the first_lsn of the next log file in sequence.

Step 2: Take a Fresh Full Backup to Reset the Chain

  • Since the existing chain is broken, perform a new full backup immediately to establish a new baseline:
  • BACKUP DATABASE [YourDBName] TO DISK = 'C:\Backups\YourDBName_Full.bak' WITH INIT, COMPRESSION;
  • Ensure the database recovery model is set to FULL (not SIMPLE) via SSMS: Right-click Database > Properties > Options > Recovery Model.
  • Schedule subsequent differential and log backups immediately after to avoid recreating the gap.

Step 3: Restore Using the Correct Sequence

  • Restore the new full backup with NORECOVERY to allow subsequent logs to be applied:
  • RESTORE DATABASE [YourDBName] FROM DISK = 'C:\Backups\YourDBName_Full.bak' WITH NORECOVERY;
  • Apply any differential backups taken after the full backup, followed by transaction logs in strict chronological order.
  • Finish with RESTORE DATABASE [YourDBName] WITH RECOVERY; only after all available logs have been applied.

Step 4: Audit for External Interference

  • Check Windows Event Viewer (Applications and Services Logs > SQL Server) for unexpected BACKUP LOG operations around the time of the gap.
  • Disable or reconfigure any third-party backup agents (e.g., Veeam, Commvault) that may be issuing log truncation commands outside your maintenance plan.

Alternative or Verification Steps

  • Verify success by running RESTORE HEADERONLY FROM DISK = 'YourLogFile.trn' and confirming the FirstLSN aligns with the LastLSN of the previously restored file with no gaps.
  • If a valid log sequence cannot be reconstructed, consider accepting data loss up to the last full/differential backup point and restoring with WITH RECOVERY directly after the differential, bypassing the broken log segment entirely.