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SQL Server Performance Best Practices for Developers


SQL Server performance tuning can be a complex process, but there are some key best practices you can follow to optimize your system. In this article, we’ll provide you with eight essential tips for improving your SQL Server performance, including how to identify bottlenecks, optimize queries, and configure memory and disk settings. By following these best practices, you can ensure your SQL Server instance runs efficiently and smoothly, providing optimal performance for your applications and users.

  1. Avoid using scalar functions in WHERE clauses.

Scalar functions, when used in WHERE clauses, can lead to performance issues because they force the SQL Server to evaluate the function for each row in the result set. This can significantly slow down the query execution, particularly when dealing with large data sets. Instead, consider using inline table-valued functions, which are more efficient and can be used to filter results in the same way as scalar functions. For example, instead of using:

SELECT * FROM Customers WHERE dbo.GetAge(BirthDate) > 18;

Use an inline table-valued function like this:

SELECT * FROM Customers c
CROSS APPLY dbo.GetAgeInline(BirthDate) Age
WHERE Age.Value > 18;

  1. Use temp tables instead of table variables.

Temp tables and table variables both serve as temporary storage for data within your T-SQL code, but temp tables generally offer better performance. Temp tables are stored in the tempdb database and have statistics, which allows the query optimizer to make better decisions regarding query execution plans. On the other hand, table variables do not have statistics, often leading to less efficient query plans.

For example, instead of using a table variable like this:

DECLARE @CustomerOrders TABLE (OrderId INT, CustomerId INT, OrderDate DATETIME);

Use a temp table:

CREATE TABLE #CustomerOrders (OrderId INT, CustomerId INT, OrderDate DATETIME);

  1. Regularly update statistics to keep query optimization accurate.

SQL Server relies on statistics to generate efficient query execution plans. Outdated or inaccurate statistics can lead to suboptimal query performance. To ensure that the query optimizer has accurate and up-to-date information, regularly update the statistics on your tables and indexes. This can be done manually using the UPDATE STATISTICS command or by enabling the “Auto Update Statistics” option in your database settings.

  1. Use the Query Store to track query performance and identify problematic queries.

The Query Store is a powerful tool in SQL Server that captures query execution plans and runtime statistics. By analyzing this data, you can identify problematic queries that are causing performance issues and optimize them accordingly. To enable the Query Store, configure its settings in your database properties, and then use the built-in reports and views to analyze query performance. For example, you can use the “Top Resource Consuming Queries” report to identify the most expensive queries in terms of CPU, memory, and I/O usage.

  1. Implement proper indexing to speed up queries.

Indexes are essential for optimizing query performance, as they allow SQL Server to quickly locate and access the required data. However, poorly designed or missing indexes can lead to slow query execution and increased resource usage. To ensure optimal performance, analyze your query workload and create appropriate indexes based on the columns and predicates used in your queries. Also, consider using the Database Engine Tuning Advisor, a built-in tool in SQL Server that recommends index and partitioning strategies based on a given workload.

  1. Enable instant file initialization to speed up database creation and growth.

By default, when SQL Server creates or grows a data file, it initializes the new space by filling it with zeroes. This process can be time-consuming, particularly for large data files. To speed up this process, enable the “instant file initialization” feature, which allows SQL Server

… and if all else fails, or you believe the issue may be SQL Server infrastructure related, please contact us to organise an obligation free quotation on a SQL Server Health check!