Query tuning is an essential skill for SQL Server database users, administrators, and developers. Writing efficient and performant queries is crucial for optimizing the overall performance of your SQL Server database. In this article, we will discuss some general guidelines and techniques to help you identify and fix problematic SQL queries.

Always Check the Execution Plan

Whether you are using SQL Server Management Studio, Azure Data Studio, or a third-party tool, it is important to always examine the query execution plan. The execution plan provides valuable insights into the query’s performance and helps you identify areas for improvement. You can learn more about creating and interpreting execution plans in these articles:

• SQL Server Execution Plan Overview
• How to Read SQL Server Graphical Query Execution Plans
• Comparison between a SQL Server Graphical Plan and Text Plan

Identify Operators with Highest Cost

When analyzing the execution plan, pay attention to the operators with the highest cost. These operators indicate potential bottlenecks in the query’s performance. By focusing on optimizing these high-cost operators, you can significantly improve the overall query performance.

Look for Warnings

During query execution, warnings may be generated for certain operations. These warnings can provide valuable insights into potential performance issues. Pay attention to warnings such as “implicit conversion” or “high memory grant” and take appropriate actions to address them.

Arrows Between Operators Provide Insight

The arrows between operators in the execution plan provide information about the estimated and actual rows, as well as the data size passed between operations. The size of the arrow indicates the amount of data and rows being transferred. Analyzing these arrows can help you identify areas where data transfer can be optimized.

Utilize the Execution Plan Properties Window

The execution plan properties window provides in-depth information about each operator in the plan. By right-clicking on an operator and selecting “Properties,” you can access detailed information that can help you understand and optimize the query execution.

Consider Index Suggestions

In some cases, the execution plan may suggest creating indexes to improve query performance. These index suggestions are shown in green text. Before creating new indexes, review the suggestions and existing indexes to avoid duplicate indexes and ensure optimal performance.

Ensure SARGABLE Queries

Most production queries include filters to reduce the number of returned rows. To efficiently use indexes, it is important to ensure that the query is SARGable. SARGable queries can effectively utilize indexes for query processing. Review your query design and make necessary code changes to ensure SARGable queries.

Consider Data Distribution

If a query runs fast sometimes and slower at other times, it may be related to data distribution and statistics. Check the statistics distribution for the tables involved in the query to understand how the data is distributed. Analyzing data distribution can help you optimize query performance.

Monitor Performance Metrics

In addition to the techniques mentioned above, there are several tools and metrics that can assist in determining query performance issues. Tools like sp_whoisactive, SQL Server First Responder Kit, and wait stats queries can help identify long-running queries, high CPU utilization, and other performance-related metrics. Consider using SQL Performance Counters, Extended Events, and Query Store for monitoring and analyzing query performance.

Explore New SQL Server Features

With each new version of SQL Server, Microsoft introduces new features to enhance query performance. Features like AI and machine learning-based intelligent query processing can adapt to your workload and make performance improvements automatically. Additionally, automatic tuning in SQL Server 2017 and later versions can identify and address query performance issues by making configuration changes automatically.

By following these tips and techniques, you can significantly improve the performance of your SQL Server queries. Remember to regularly monitor and optimize your queries to ensure optimal database performance.