What Is Log Shipping?

Definition: Log Shipping

Log shipping is a high-availability and disaster recovery technique used in SQL Server and other database management systems to automatically send and apply transaction log backups from a primary database to one or more secondary databases. This process ensures data redundancy, failover support, and disaster recovery, helping organizations maintain database availability in case of failures.

Understanding Log Shipping

Log shipping works by regularly backing up the transaction logs from a primary database and restoring them to a secondary (standby) database. This allows the secondary database to stay nearly in sync with the primary database. In the event of failure, the secondary database can take over, minimizing downtime.

Key Characteristics of Log Shipping

• Automated Backup and Restore – Periodically copies transaction logs from the primary to the secondary server.
• Disaster Recovery Solution – Provides a failover mechanism in case of database failure.
• Minimal Data Loss – Ensures a near real-time copy of the database.
• One-Way Data Replication – Secondary databases remain read-only or in standby mode.
• Supports Multiple Secondary Databases – Can be configured to ship logs to multiple standby servers.

How Log Shipping Works

Log shipping involves three main steps:

1. Transaction Log Backup (Primary Server)

• The primary database generates transaction log backups at scheduled intervals.
• These backups contain a record of all committed transactions.

2. Copying Transaction Logs (Network Transfer)

• The transaction log backups are transferred to the secondary server(s) via a shared network folder.
• The frequency of log shipping depends on the backup schedule.

3. Restoring Transaction Logs (Secondary Server)

• The secondary server restores the copied transaction logs, keeping the database up to date.
• The database can be set to Standby Mode (read-only) or No Recovery Mode (fully synchronized for failover).

Log Shipping Architecture

Log shipping typically involves three main components:

1. Primary Server (Source Database) – Generates transaction log backups.
2. Secondary Server (Destination Database) – Receives and restores transaction logs.
3. Monitor Server (Optional) – Tracks log shipping status, failures, and alerts administrators.

Benefits of Log Shipping

1. High Availability and Disaster Recovery

Provides an automated failover mechanism, reducing downtime in case of primary database failure.

2. Minimal Data Loss

Regular transaction log backups ensure near real-time synchronization between primary and secondary databases.

3. Load Balancing for Read-Only Queries

The secondary database can be kept in standby mode, allowing read-only queries to distribute database load.

4. Simple and Cost-Effective Solution

Unlike database mirroring or Always On availability groups, log shipping requires minimal setup and no expensive licensing.

5. Supports Multiple Secondary Databases

Log shipping allows replication of transaction logs to multiple secondary databases, improving redundancy.

Limitations of Log Shipping

1. No Automatic Failover

Unlike Always On Availability Groups, log shipping requires manual intervention for failover.

2. Potential Data Loss

If the primary server fails before recent logs are shipped, data loss may occur.

3. Latency in Data Synchronization

The secondary database is not in real-time sync due to the scheduled nature of log backups.

4. Read-Only Secondary Database

The secondary database is typically read-only or unavailable until restored completely.

Log Shipping vs. Other High-Availability Solutions

How to Set Up Log Shipping in SQL Server

Prerequisites:

• SQL Server installed on primary and secondary servers.
• Sufficient storage space for transaction log backups.
• Network file share for log file transfers.

Step 1: Configure the Primary Database for Log Shipping

1. Open SQL Server Management Studio (SSMS).
2. Right-click the primary database, select Properties > Transaction Log Shipping.
3. Check Enable this as a Primary Database in Log Shipping Configuration.
4. Configure the backup schedule and destination folder.
5. Click OK to apply settings.

Step 2: Configure the Secondary Database

1. On the secondary server, create a new database (in No Recovery Mode).
2. Right-click the database, go to Properties > Log Shipping.
3. Set up log restore settings and define standby or no recovery mode.
4. Apply changes and start log shipping synchronization.

Step 3: Monitor Log Shipping Status

• Use SQL Server Agent Jobs to track backup, copy, and restore operations.
• Set up alerts and notifications for failures.

Best Practices for Log Shipping

1. Schedule Log Backups Based on RTO & RPO

• Lower backup intervals (5-10 minutes) reduce data loss risk.
• Higher intervals reduce system overhead but increase potential data loss.

2. Use Network Compression for Faster Log Transfers

• Compress transaction logs to reduce transfer time.

3. Automate Monitoring and Alerts

• Configure SQL Server Agent Jobs to notify administrators of failures.

4. Test Failover Regularly

• Perform manual failover tests to ensure secondary databases are operational.

5. Secure Transaction Log Backups

• Use encryption and access controls for stored logs.

Use Cases of Log Shipping

1. Disaster Recovery and Failover Planning

Ensures a backup database is available in case of server failure.

2. Reporting and Read-Only Queries

Provides a standby database for generating reports and running analytics without affecting the primary database.

3. Migrating to a New Server

Assists in database migration by maintaining a synchronized copy on the new server.

4. Load Balancing for Large Applications

Allows multiple secondary databases to distribute workloads.

Future of Log Shipping

With advancements in cloud computing and SQL Server Always On, log shipping is gradually being replaced by more automated high-availability solutions. However, it remains a cost-effective and reliable option for businesses that require simple disaster recovery and secondary database replication.

Frequently Asked Questions Related to Log Shipping