Patching and Updates for the SQL Database Engine

Maintaining an up-to-date SQL Server instance is crucial for security, performance, and stability. This section provides comprehensive guidance on applying patches, service packs, and cumulative updates to your SQL Database Engine.

Understanding SQL Server Updates

Microsoft periodically releases updates for SQL Server to address security vulnerabilities, fix bugs, and introduce new features. These updates come in several forms:

• Cumulative Updates (CUs): These are the most frequent updates and include all previously released fixes as well as new fixes. They are recommended for all customers.
• Service Packs (SPs): Less frequent than CUs, SPs are major updates that include a collection of fixes and sometimes new features. They are typically released for major SQL Server versions.
• Security Updates (SUs): These focus specifically on critical security vulnerabilities.

Patching Strategies

Choosing the right patching strategy depends on your environment's requirements for uptime, risk tolerance, and testing capabilities.

1. Regular Patching Schedule

Implement a regular schedule (e.g., monthly, quarterly) to apply the latest Cumulative Updates. This proactive approach helps minimize the attack surface and keeps your system running smoothly.

2. Pre-Patching Testing

Always test patches in a non-production environment that mirrors your production setup before applying them to production servers. This includes:

• Testing application compatibility.
• Verifying performance impacts.
• Confirming backup and restore operations.

3. Phased Rollout

For critical production environments, consider a phased rollout. Start with less critical servers or development/staging environments, monitor them closely, and then proceed to more critical production systems.

Applying Updates

The process for applying updates generally involves downloading the appropriate patch and running the installer. However, best practices should always be followed.

Pre-Application Checklist:

1. Backup Everything: Ensure you have recent, verified backups of all your databases and the `master` and `msdb` system databases.
2. Review Release Notes: Carefully read the release notes for the specific update to understand any prerequisites, known issues, or behavioral changes.
3. Check Compatibility: Verify that the update is compatible with your operating system and any other installed software.
4. Schedule Downtime: Plan for a maintenance window, as SQL Server services will need to be restarted, potentially causing downtime.
5. Document the Process: Keep detailed records of the update applied, the date, and any issues encountered.

Steps to Apply a Cumulative Update:

1. Download the latest CU from the official Microsoft SQL Server downloads page.
2. Ensure all SQL Server services (Database Engine, Agent, etc.) are running.
3. Run the downloaded installer executable.
4. Follow the on-screen prompts. The installer will typically detect your installed SQL Server instance.
5. The installer will update the relevant binaries.
6. After the installation completes, restart the SQL Server services.
7. Verify the new version by running:

   SELECT @@VERSION;

8. Perform basic connectivity tests and application checks.
9. Run a full backup of your databases after a successful patch application.

Rollback Strategy

Having a clear rollback plan is essential in case a patch causes unexpected problems. The primary rollback mechanism is restoring your databases from the backups taken before the patch was applied. In some rare cases, it may be possible to uninstall the patch from Add/Remove Programs, but restoring from backup is the recommended and most reliable method.

Specific Scenarios

• Clustered Environments: Patching SQL Server Failover Cluster Instances requires careful coordination across all nodes in the cluster. Typically, you patch one node at a time, failover, and then patch the remaining nodes.
• Always On Availability Groups: For Availability Groups, it's recommended to patch secondary replicas first, then failover to a patched secondary, and then patch the former primary.

Tip: Automating the patching process using tools like Microsoft Endpoint Configuration Manager (MECM) or custom scripts can improve consistency and reduce manual errors, especially in large environments.