Understanding SQL Server Execution Plan for Dev

As a developer, you must have come across the term SQL Server Execution Plan. It is an important aspect of SQL Server that can have a significant impact on the performance of your queries. In this journal article, we will cover everything you need to know about SQL Server Execution Plan.

What is SQL Server Execution Plan?

SQL Server Execution Plan is a graphical representation of the steps involved in executing a query in SQL Server. It shows how the database engine will access the required data to satisfy the query. Execution Plan consists of a series of operators that perform various tasks to retrieve the data. Understanding the Execution Plan can help you optimize your query and improve its performance.

Let’s take a look at an example of Execution Plan:

Understanding the Execution Plan table

The Execution Plan table consists of several columns that provide information about how the query is executed. Here’s what each column means:

• Operator: The operator used to retrieve the data.
• EstimateRows: The estimated number of rows that will be returned by the operator.
• EstimateIO: The estimated number of IO operations required to retrieve the data.
• EstimateCPU: The estimated amount of CPU time required to retrieve the data.
• TotalSubtreeIO: The total number of IO operations required to retrieve the data, including child operations.
• TotalSubtreeCPU: The total amount of CPU time required to retrieve the data, including child operations.
• OutputList: The columns returned by the operator.

Why is Execution Plan important?

Execution Plan is important because it helps you identify the bottlenecks in your query. You can use the information provided by the Execution Plan to optimize your query and improve its performance. Without understanding Execution Plan, it is difficult to know where the performance issues are in your query.

How to view Execution Plan?

You can view Execution Plan in SQL Server Management Studio by clicking on the “Include Actual Execution Plan” button. This will execute the query and display the Execution Plan in a separate tab.

Interpreting Execution Plan

Interpreting Execution Plan can be overwhelming, but don’t worry, we’ve got you covered. We will walk you through the basic steps involved in interpreting Execution Plan.

Step 1: Identify the operator

The first step in interpreting Execution Plan is to identify the operator used to retrieve the data. The operator is usually found at the top of the Execution Plan table. In our example, the operator is “Clustered Index Scan”.

Step 2: Look at the estimated rows

The second step is to look at the estimated rows. This tells you how many rows the operator is expected to retrieve. In our example, the estimated rows are 1.

Step 3: Look at the estimated IO and CPU

The third step is to look at the estimated IO and CPU. This tells you how much IO and CPU time the operator is expected to use. In our example, the estimated IO is 0.003125 and the estimated CPU is 0.0001042.

Step 4: Look at the total subtree IO and CPU

The fourth step is to look at the total subtree IO and CPU. This tells you how much IO and CPU time the operator and its child operators are expected to use. In our example, the total subtree IO is 0.003125 and the total subtree CPU is 0.0001042.

Step 5: Look at the OutputList

The fifth and final step is to look at the OutputList. This tells you what columns will be returned by the operator. In our example, the OutputList includes CustomerID, CompanyName, ContactName, ContactTitle, Address, City, Region, PostalCode, Country, Phone, and Fax.

FAQs

Q1: What is the difference between estimated and actual Execution Plan?

The estimated Execution Plan is generated by SQL Server before the query is executed, whereas the actual Execution Plan is generated after the query is executed. The estimated Execution Plan is based on statistics and assumptions regarding the data, whereas the actual Execution Plan is based on the actual data.

Q2: How do I analyze Execution Plan?

You can analyze Execution Plan by looking for operators that have high IO or CPU usage, high estimated or actual rows, or large number of child operators. These are usually the bottlenecks in your query and need to be optimized.

Q3: Can Execution Plan be wrong?

Yes, Execution Plan can be wrong if the statistics used by SQL Server are outdated or incorrect. It is important to regularly update the statistics to ensure accurate Execution Plan.

Q4: How to optimize Execution Plan?

You can optimize Execution Plan by identifying the bottlenecks in your query and optimizing the operators that are causing them. This may involve creating indexes, changing the query structure, or rewriting the query altogether.

Q5: How to improve query performance using Execution Plan?

You can improve query performance using Execution Plan by optimizing the bottlenecks in your query. By improving the operators that are causing the bottlenecks, you can significantly improve the performance of your query.

Conclusion

SQL Server Execution Plan is an important aspect of SQL Server that can have a significant impact on the performance of your queries. By understanding Execution Plan, you can optimize your queries and improve their performance. We hope this article has helped you understand Execution Plan better.