Understanding SQL Statistics: Is It OK to Drop Them?
In the world of SQL Server management, one question that often arises is whether it’s acceptable to drop SQL statistics, especially when performing maintenance tasks such as altering columns from nullable to not nullable. This post addresses this question and provides clarity on the topic.
The Problem: Managing SQL Statistics During Alterations
When you work on modifying database schema, particularly altering columns, there are various associated tasks – including dropping and recreating objects like statistics. You might use tools like SQL Compare, which assists in generating scripts for these changes. However, many users have noticed that such tools often do not include statistics in their generated scripts. This raises a critical question: Is it safe to drop statistics, or do we risk impacting database performance?
The Solution: Understanding SQL Server’s Handling of Statistics
Best Practices with SQL Statistics
When it comes to handling statistics in SQL Server, there are established best practices:
- Auto Creation/Update: SQL Server is designed to automatically create and update statistics. This means that if SQL Server detects that it needs statistics for query optimization, it will generate them on demand.
- Maintenance Plans: While it’s common to see recommendations to update statistics as part of a regular maintenance plan, this action may not be necessary. If auto-creation and auto-update settings are enabled, SQL Server manages this process effectively on its own.
Why Dropping Statistics Might Not Be a Concern
- Automatic Handling: If you drop SQL statistics, SQL Server will generally compensate for it by creating new statistics as needed during query execution.
- Performance Management: Statistics play a crucial role in query optimization and execution plans, but SQL Server’s ability to generate these statistics on-the-fly means that dropping them won’t necessarily harm your database performance.
Recommendations for Database Administrators
- Enable Auto Settings: Ensure that both auto-create and auto-update statistics options are enabled. This is critical for maintaining optimal performance when making schema changes.
- Monitor Performance: After making changes that involve dropping statistics, monitor your database performance to ensure that SQL Server is effectively creating the necessary statistics as queries are executed.
- Review Maintenance Plans: While it might be tempting to include explicit statistics updates within maintenance plans, consider whether this is needed given SQL Server’s built-in capabilities.
Conclusion
In summary, dropping SQL statistics during schema alterations is generally safe, provided that SQL Server’s auto-create and auto-update settings are in play. This auto-management allows for a smooth process without worrying excessively about manual statistics maintenance. Ultimately, effective monitoring and understanding of SQL Server’s internal mechanisms will help ensure your database remains performant and efficient over time.
By adopting these best practices, you can simplify your database operations and focus on maintaining its integrity without the unnecessary burden of manually managing statistics.