Breaking Changes Between Versions

Breaking Changes Between SQL Server Versions

Upgrading from one version of SQL Server to another can be an exciting, yet challenging, task. While newer versions typically come with enhanced features, performance improvements, and better security, they can also introduce breaking changes. These breaking changes can affect applications, queries, and even system configurations. For database administrators (DBAs) and developers, understanding these changes is crucial to ensuring a smooth transition and avoiding downtime.

In this comprehensive guide, we will walk you through the key concepts and details about breaking changes between SQL Server versions, identify which changes you need to be aware of, and provide detailed guidance on how to mitigate or resolve issues. This guide will also help you understand the upgrade paths and steps involved, enabling you to plan a successful upgrade with minimal disruptions.

1. Introduction to Breaking Changes

In the context of SQL Server, breaking changes refer to changes made in a new version that are not backward-compatible with previous versions. These changes can lead to errors, degraded performance, or unexpected behaviors in existing applications or database environments that were designed for earlier versions of SQL Server.

Breaking changes are typically introduced when Microsoft enhances the database engine, adds new features, or refactors existing functionality. These changes may impact the following:

SQL Syntax and Compatibility: Changes in how SQL queries or scripts are executed.
Data Types: Alterations to how certain data types are handled.
Stored Procedures and Functions: Modifications or removals of system stored procedures or functions.
Indexes and Optimizations: Differences in query execution plans or index optimizations that affect performance.
Security and Authentication: Adjustments to authentication methods, encryption standards, or user roles.
Deprecated Features: Features that are removed or no longer supported in the new version.

Breaking changes can sometimes be subtle and only noticeable after significant testing. Therefore, it is essential to carefully read Microsoft’s release notes and upgrade documentation when moving to a new SQL Server version.

2. Common Types of Breaking Changes

There are various types of breaking changes that can occur between different SQL Server versions. Understanding each type can help you mitigate risks during the upgrade.

2.1. SQL Syntax and Query Behavior Changes

SQL syntax changes can often break existing queries or scripts. Microsoft sometimes modifies how certain commands or statements are processed by the SQL Server engine. Some of the common syntax changes include:

Keyword Changes: New reserved keywords or renamed features may conflict with previously used identifiers. For example, the ROWGUIDCOL keyword became a reserved keyword in SQL Server 2012, which could affect existing schemas.
T-SQL Behavior Changes: The behavior of specific T-SQL commands, such as MERGE, SELECT INTO, or INSERT, may change. These changes could lead to errors or unexpected results if an application relies on older behavior.
Query Optimizer Changes: SQL Server often updates its query optimizer in newer versions to improve performance. However, this can lead to changes in the execution plan, resulting in performance degradation for certain queries.

2.2. Data Type and Storage Changes

Changes in data type behavior or storage formats can be a significant cause of breaking changes. These changes could affect the way data is stored, retrieved, or processed in SQL Server.

New Data Types: New versions of SQL Server may introduce new data types (e.g., DATE, DATETIME2, XML, GEOGRAPHY, etc.). While these new types can be beneficial, they might also cause compatibility issues with older applications if not properly handled.
Changes to Existing Data Types: For example, SQL Server 2012 introduced changes to how VARCHAR(MAX) and TEXT data types are handled, leading to possible truncation or conversion errors.
Storage and Indexing: Changes to how indexes are created or how certain data types are stored (e.g., row compression, page compression, or in-memory tables) may require alterations to existing database designs.

2.3. Deprecated and Removed Features

When upgrading to a newer SQL Server version, you may encounter deprecated features or functionalities that are no longer available. These can often lead to immediate problems when your application tries to use them.

Deprecated Features: Microsoft flags certain features as deprecated when they are on the verge of being removed in future versions. Features like FILESTREAM, SQLCLR, or certain system stored procedures might have limited support and could behave differently in new versions.
Removed Features: Features that were once supported in earlier versions might be entirely removed from a new version. For instance, xp_cmdshell or replication features may not be supported in the same manner or could be removed.
Deprecated Functions: Functions or system stored procedures may no longer function as expected, and new alternatives are often introduced. For example, SQL Server 2016 removed support for sp_rename on tables with indexes.

2.4. Authentication and Security Changes

SQL Server frequently evolves its authentication and security model. These changes can cause existing applications or users to encounter issues during authentication or role-based access control.

Windows Authentication Changes: In newer versions of SQL Server, there might be changes in how Windows authentication is processed. For example, Windows authentication modes like Mixed Mode (SQL Server and Windows Authentication) might need to be reconfigured.
Encryption and SSL Changes: SQL Server versions may enforce stronger encryption protocols, SSL/TLS versions, or move towards more modern hashing algorithms, which could break compatibility with older applications or systems that use outdated standards.
Login and User Mappings: Changes in the way logins, users, or groups are handled could lead to permission issues or authentication failures after upgrading to a newer version.

2.5. Performance and Query Execution Changes

As SQL Server versions evolve, optimizations are made to improve performance, but these optimizations can also lead to unexpected behavior in existing queries.

Query Execution Plans: The SQL Server query optimizer might change between versions, leading to different execution plans for the same query. While this can result in better performance, it may also cause some queries to perform worse.
Indexing and Storage Engine Changes: SQL Server might introduce new ways to manage indexes, alter the behavior of existing ones, or introduce new storage engines (e.g., in-memory OLTP). These changes can cause issues if applications depend on specific indexing strategies.
Parallelism and Concurrency: Newer versions may adjust how SQL Server handles parallel queries, locking, or transaction isolation levels, potentially affecting query results and performance.

3. Addressing Breaking Changes in SQL Server Versions

When migrating between SQL Server versions, it’s important to address breaking changes by thoroughly planning and testing the upgrade process.

3.1. Compatibility Level

SQL Server has a compatibility level setting that determines how a database behaves in terms of query processing and features. The compatibility level can help address some breaking changes by maintaining older behavior when migrating to a new version.

Set Compatibility Level: During the upgrade, you can adjust the database’s compatibility level to maintain compatibility with an older version of SQL Server. For example, setting the compatibility level to 110 (SQL Server 2012) on a database in SQL Server 2016 will allow it to behave similarly to SQL Server 2012.
Test Compatibility Levels: Always test how your application behaves at different compatibility levels. Be aware that some features are tied to specific versions, and changing the compatibility level may not fully address all breaking changes.

3.2. Application and Query Testing

It is essential to test all applications and queries before migrating to a new SQL Server version. You can use tools like SQL Server Profiler or Extended Events to monitor queries and identify performance issues caused by breaking changes.

Regression Testing: Run all regression tests on your applications and scripts to ensure that no functionality is broken due to the upgrade.
Use Query Store: SQL Server’s Query Store can help capture and analyze query performance. It is useful for comparing performance in the old and new versions to identify problematic queries.

3.3. Deprecated and Removed Feature Resolution

Identify deprecated and removed features during the upgrade assessment phase and plan accordingly. Microsoft provides extensive documentation on deprecated features and removal notices for each SQL Server version.

Replace Deprecated Features: Before upgrading, find alternatives for deprecated features. For example, replace SQLCLR usage with native T-SQL or find alternatives for deprecated system stored procedures.
Code Refactoring: If certain functionality is removed in the new version, refactor or rewrite parts of your application that depend on those features.

3.4. Security and Authentication Testing

Verify Logins and User Mappings: After migration, verify that logins and user mappings are intact and functioning as expected.
Update Security Protocols: If SSL/TLS or encryption methods have changed, ensure that all security protocols are updated across your applications and infrastructure.
Use Testing Tools: Utilize Microsoft’s SQL Server Data Tools (SSDT) and other security auditing tools to check for security issues after the upgrade.

3.5. Monitor and Optimize Post-Upgrade

After completing the upgrade, it’s important to monitor the performance and stability of the SQL Server instance.

Monitor Resource Usage: Use SQL Server Management Studio (SSMS) or SQL Server Performance Monitor to monitor CPU, memory, and I/O usage.
Analyze Query Performance: Continually monitor queries and execution plans to ensure that the new version of SQL Server is performing optimally.

Breaking changes between versions of SQL Server can be a significant challenge, but with proper planning and testing, they can be addressed effectively. Understanding the nature of these changes and taking the necessary steps to mitigate potential issues is crucial for a successful migration or upgrade.

Stay up-to-date with Microsoft’s release notes and change logs for each SQL Server version.
Use compatibility levels, testing tools, and application refactoring to ensure compatibility with newer versions.
Take advantage of SQL Server’s built-in features (such as the Query Store, Extended Events, and Compatibility Levels) to help monitor, test, and address any issues during the upgrade.

With careful preparation, testing, and monitoring, you can minimize the impact of breaking changes and ensure that your systems remain stable and perform efficiently after migrating to a new version of SQL Server.

5. Deep Dive into Specific Breaking Changes Across Versions

In addition to the general concepts discussed previously, it’s essential to dive deeper into specific breaking changes that can occur between different versions of SQL Server. This deeper analysis will help you identify specific challenges you may encounter when upgrading from one version to another. Here’s a breakdown of breaking changes across different versions of SQL Server:

5.1. SQL Server 2008 to 2012

Upgrading from SQL Server 2008 to SQL Server 2012 involves several notable breaking changes:

New Reserved Keywords: SQL Server 2012 introduced new reserved keywords like ROWGUIDCOL. If your code or table structures use these keywords as identifiers (for example, column names), you will need to rename these objects or wrap them in square brackets to prevent issues.
Changes to Data Types: SQL Server 2012 deprecated the TEXT and NTEXT data types and recommended migrating to VARCHAR(MAX) and NVARCHAR(MAX) for better performance and support.
SQL Server Agent: The SQL Server Agent in SQL Server 2012 saw changes in how jobs are executed, impacting older jobs or scripts that might use outdated configurations or parameters.
Changes in Functions: SQL Server 2012 introduced the TRY_CAST() and TRY_CONVERT() functions. These are safer alternatives to CAST() and CONVERT(), as they return NULL instead of throwing an error when the conversion fails. If your application used strict casting/conversion operations, these changes might require modification.
Columnstore Indexes: The introduction of columnstore indexes in SQL Server 2012 was a game-changer for analytics workloads. While they provided enormous performance improvements, they also required specific schema configurations and data types that may not have been present in earlier versions, leading to compatibility issues.

5.2. SQL Server 2012 to 2014

SQL Server 2014 introduced several new features, some of which could lead to breaking changes, including:

In-Memory OLTP: SQL Server 2014 introduced In-Memory OLTP (also known as Hekaton), a new memory-optimized table technology that dramatically changes the way data is stored and processed. Applications that were not built with In-Memory OLTP in mind could face compatibility issues, especially when working with large tables or workloads that require massive amounts of data processing.
Delayed Durable Transactions: SQL Server 2014 introduced the concept of delayed durable transactions, which allows for improved performance by deferring transaction log flushes. However, if applications were expecting transactions to be immediately durable, this feature might cause issues. Ensure to test for this setting and evaluate if it impacts your system.
Improved Query Optimizer: The query optimizer received improvements in SQL Server 2014, which could affect the execution plans and performance of queries that ran without issues on previous versions. Applications relying on certain execution plans may require adjustments.

5.3. SQL Server 2014 to 2016

SQL Server 2016 introduced even more innovative features, but along with them came some breaking changes:

Always Encrypted: SQL Server 2016 introduced Always Encrypted, a feature that allows data to be encrypted in transit and at rest. While this feature enhances security, it may break existing applications or cause performance issues for applications that have not been designed with Always Encrypted in mind. If your application requires interaction with encrypted columns, you will need to ensure that proper encryption keys are managed and permissions are set correctly.
Dynamic Data Masking: SQL Server 2016 also introduced Dynamic Data Masking to protect sensitive data by obfuscating it in certain scenarios. While this adds an extra layer of security, older applications might encounter issues if the new feature is not correctly configured.
JSON Support: SQL Server 2016 introduced support for JSON data manipulation. Although not a true breaking change, applications that previously relied on XML for data storage or parsing might need to be updated to accommodate this new data type, which could result in some compatibility issues.
Deprecated Features: In SQL Server 2016, several features became deprecated or were removed, such as the sp_rename stored procedure on objects that are part of indexed views and certain replication features. Applications and databases that used these features need to be refactored to ensure continued functionality.

5.4. SQL Server 2016 to 2017

SQL Server 2017 was another leap forward, especially with the introduction of cross-platform support (Linux support), but it also introduced some breaking changes:

Cross-Platform Compatibility: With SQL Server 2017 supporting both Linux and Windows, there are potential breaking changes if your database or application depends on OS-specific functionality, such as file paths or Windows-integrated authentication. These issues need to be tested thoroughly if you’re running cross-platform environments.
SQL Server Machine Learning: SQL Server 2017 introduced enhanced integration with Python and R for machine learning capabilities. However, if your existing SQL Server environment uses older versions of these libraries, or if the application code uses specific machine learning models, these dependencies need to be updated to avoid incompatibility.
Graph Database Features: SQL Server 2017 introduced graph databases and graph extensions to enable complex relationships between data. While this is an exciting feature, applications relying on traditional relational schemas may encounter compatibility problems when they need to incorporate graph structures.

5.5. SQL Server 2017 to 2019

SQL Server 2019 brings several modern features, but it’s not without potential breaking changes:

Big Data Clusters: SQL Server 2019 introduces Big Data Clusters for integrating SQL Server with Hadoop and Spark. Organizations not previously working with big data may face compatibility issues with storage, networking, and data retrieval mechanisms. Migrating to SQL Server 2019 might require substantial changes to the architecture of your environment if Big Data Clusters are being used.
Intelligent Query Processing (IQP): SQL Server 2019 enhanced Intelligent Query Processing features like Adaptive Joins, Interleaved Execution, and Batch Mode for Scalar UDFs. While these features offer improved performance, they might alter query execution and impact workloads that previously worked on older versions. Performance testing should be done after upgrading to verify no regressions occur.
In-Memory Database Improvements: SQL Server 2019 introduces new in-memory database improvements like Accelerated Database Recovery (ADR) and improvements to the In-Memory OLTP engine. If your application was relying on specific in-memory features from SQL Server 2017 or earlier, you should revalidate its performance post-upgrade.

6. Managing and Mitigating Breaking Changes During Upgrade

When migrating between SQL Server versions, proactively managing breaking changes is critical. Here’s a detailed guide on how to address and mitigate issues:

6.1. Perform a Comprehensive Pre-Upgrade Assessment

Before jumping into the migration process, perform a thorough assessment of your current environment:

Audit Features in Use: Identify which features, functions, stored procedures, and configurations in your environment are potentially affected by breaking changes.
Review SQL Scripts and Queries: Use tools like SQL Server Management Studio (SSMS) or SQL Server Profiler to review existing queries, jobs, and scripts. Look for usage of deprecated features, SQL syntax issues, and compatibility problems.
Test Compatibility Levels: Test how your application behaves at different compatibility levels. Microsoft provides a compatibility level chart that helps you understand what functionality will be retained and what might change.

6.2. Use the SQL Server Upgrade Advisor

SQL Server provides an Upgrade Advisor tool (or SQL Server Data Migration Assistant (DMA) in more recent versions) that scans your environment for potential issues. The advisor checks for deprecated features, unsupported features, and other issues that may arise during the upgrade. It helps you:

Identify breaking changes based on your current SQL Server version.
Provide recommendations on how to resolve compatibility issues.
Estimate the time and effort required for the upgrade process.

6.3. Address Deprecated Features

If your environment uses deprecated features, you should replace them with supported alternatives. Common approaches include:

Replace deprecated functions or stored procedures: Microsoft provides a comprehensive list of deprecated and removed features in their documentation. If your system uses these features, refactor the code to rely on the recommended replacements.
Migrate to newer data types: If your database uses deprecated data types (e.g., TEXT, NTEXT, IMAGE), consider migrating to VARCHAR(MAX), NVARCHAR(MAX), or VARBINARY(MAX).
Refactor application code: Often, upgrading SQL Server also means upgrading the application code. Modify your code to leverage new SQL Server features, remove dependency on deprecated elements, and adjust to the changes introduced by the new version.

6.4. Test Thoroughly in a Staging Environment

Always perform extensive testing in a staging environment that mirrors your production setup. This includes:

Performance Testing: Run both old and new workloads in the staging environment to ensure that the performance of your application does not degrade.
Functional Testing: Test all critical business functionalities to ensure that no features break. This testing should include integration testing, user acceptance testing, and regression testing.
Error Logging and Monitoring: Set up error logging and monitoring to catch unexpected issues early in the upgrade process.

Upgrading SQL Server to a newer version offers enhanced features, performance improvements, and security updates. However, the process is not without its challenges, particularly when it comes to breaking changes. Understanding what these changes entail and proactively addressing potential issues can help ensure a smooth migration.

By thoroughly assessing your environment, testing compatibility, addressing deprecated features, and leveraging tools like the SQL Server Upgrade Advisor and DMA, you can mitigate many of the risks associated with breaking changes. Additionally, remember that thorough testing, especially in a staging environment, is key to ensuring that your upgrade does not disrupt business operations.

In the end, a successful upgrade to a newer version of SQL Server can provide your organization with enhanced capabilities, improved performance, and better scalability — all essential for staying competitive in today’s data-driven landscape.