The Transaction Log for Database is Full Due to log_backup

The transaction log for database 'Database_Name' is full due to 'LOG_BACKUP'.

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This error occurs when the database is in FULL or BULK_LOGGED recovery model and transaction log backups are not being taken, preventing the log from truncating. Here this post explains the cause of the error, how to fix it safely, and how to prevent it from happening again

Getting Started

One of the most common and disruptive errors faced by SQL Server administrators is:

The transaction log for database 'Database_Name' is full due to 'LOG_BACKUP'.

When this error occurs, write operations to the database can fail, applications may stop responding, and system performance can degrade rapidly. Understanding why this happens and how to resolve it correctly is essential for maintaining database health and availability.

Let's understand what is transaction log

What Is a Transaction Log?

The transaction log in SQL Server records every change made to the database. It is critical for:

• Transaction rollback
• Crash recovery
• Point-in-time restore
• High availability and replication features

Unlike data files, the transaction log is written sequentially and cannot reuse space until SQL Server determines it is safe to do so. This process is called log truncation.

Why Does the LOG_BACKUP Error Occur?

This error specifically indicates that:

• The database is using the FULL or BULK_LOGGED recovery model
• SQL Server is waiting for a transaction log backup
• No recent log backup has occurred, so the log cannot truncate

As a result, the transaction log continues to grow until it runs out of space.

Identifying the Recovery Model

The recovery model determines how transaction logs are managed. You can check it using:

SELECT name, recovery_model_desc
FROM sys.databases
WHERE name = 'DatabaseName';

• FULL: Requires regular transaction log backups
• BULK_LOGGED: Requires log backups (with minimal logging for bulk ops)
• SIMPLE: Log truncation happens automatically

The LOG_BACKUP error only occurs in FULL or BULK_LOGGED recovery models.

The Correct Way to Resolve the Issue

Take a Transaction Log Backup

The safest and recommended solution is to immediately back up the transaction log:

BACKUP LOG DatabaseName
TO DISK = 'D:\SQLBackups\DatabaseName_Log.trn'
WITH INIT;

This action:

• Truncates inactive portions of the log
• Frees log space
• Restores normal database operations

In most cases, this single step resolves the issue instantly.

Shrink the log file

Only do this after a log backup if disk space is still an issue:

USE DatabaseName;
DBCC SHRINKFILE (DatabaseName_log, 1024); -- size in MB

Shrinking should only be done occasionally. Repeated shrinking and regrowth leads to fragmentation and poor performance. To know more how to shrink database visi my previous post(Shrink The Log File In SQL Server)

Alternative Approach for Non-Production Databases

In development or test environments where point-in-time recovery is not required, switching to SIMPLE recovery may be appropriate:

ALTER DATABASE DatabaseName SET RECOVERY SIMPLE;

This:

• Breaks the log backup chain
• Allows SQL Server to reuse log space automatically
• Prevents the error from recurring

This approach is not recommended for production databases that require full recovery options.

Preventing the Error in the Future

Prevention is straightforward:

1. Schedule regular transaction log backups
2. Typical frequency:
   • Production: every 5–15 minutes
   • Lower-risk systems: every 30–60 minutes

These backups can be configured using:

• SQL Server Agent jobs
• Maintenance plans
• Third-party backup tools

Without log backups, this error will inevitably return.

When a Log Backup Is Not Enough

In rare cases, the log may still not truncate after a backup. You can identify the reason using:

SELECT name, log_reuse_wait_desc
FROM sys.databases
WHERE name = 'DatabaseName';

Common causes include:

• Long-running transactions
• Replication
• Always On Availability Groups

Each requires a targeted investigation. Common values:

• ACTIVE_TRANSACTION
• REPLICATION
• AVAILABILITY_REPLICA

Investigate accordingly.

Summary

The “transaction log is full due to LOG_BACKUP” error is not a failure—it is a safeguard. SQL Server is protecting your ability to recover data, but it depends on proper log backup management.

Thanks