Demystifying SQL Server Query Store: A Guide to Performance Analysis and Troubleshooting
Introduction
In the world of databases, performance analysis and troubleshooting are critical tasks for database administrators (DBAs). The SQL Server Query Store is a powerful tool within the SQL Server database engine that helps DBAs in analyzing and troubleshooting query performance. In this guide, we will dive deep into the SQL Server Query Store, demystifying its features and providing a step-by-step approach to performance analysis and troubleshooting.
Understanding the SQL Server Query Store
The SQL Server Query Store was introduced in SQL Server 2016 as a feature that provides insights into query performance and allows for efficient troubleshooting. It captures details about the queries executed on a database, including their execution plans, runtime statistics, and historical information. With this information, DBAs can identify performance bottlenecks, query regressions, and make data-driven decisions to improve overall performance.
Key Components of the Query Store
The SQL Server Query Store comprises three key components:
1. Query Store DMVs (Dynamic Management Views): These views allow you to retrieve information about the state of the Query Store, including captured queries, their execution plans, and runtime statistics. Examples of Query Store DMVs include sys.query_store_query, sys.query_store_plan, and sys.query_store_runtime_stats.
2. Query Store Reports: SQL Server Management Studio (SSMS) provides built-in reports that leverage Query Store DMVs to present visual representations of query performance data. These reports make it easier to analyze trends, identify top queries, and compare execution plans.
3. Query Store Configuration Options: SQL Server provides several configuration options that enable you to customize the behavior of the Query Store. These options include settings for data retention, query capture mode, performance thresholds, and more.
Enabling and Configuring Query Store
To begin using the Query Store in your SQL Server database, you first need to enable and configure it. Here are the steps to do so:
1. Enable Query Store: Open SSMS, connect to your SQL Server instance, and right-click on the target database. Select “Properties” and navigate to the “Query Store” tab. Check the box that says “Enable Query Store” and click “OK”.
2. Configure Query Store Options: After enabling Query Store, you can configure various options as per your requirements. These include retention period, query capture mode, and data size. It is important to choose appropriate values for these options to optimize performance and storage utilization.
Query Performance Analysis using Query Store
Now that Query Store is enabled and configured, let’s explore how we can leverage its features to analyze query performance.
Identifying Top Queries
One of the key benefits of Query Store is the ability to identify top queries in terms of resource consumption. The following steps will guide you through this process:
1. Open SSMS, connect to your SQL Server instance, and expand the target database.
2. Navigate to the “Query Store” node and expand it to reveal the “Queries” sub-node.
3. Right-click on the “Queries” sub-node and select “Top Resource Consuming Queries”.
4. In the “Top Resource Consuming Queries” dialog, you can specify the number of top queries to analyze and the metric you want to consider (CPU time, logical reads, or duration).
5. Click “OK” to generate the report, which will show the top queries based on the specified metric.
Comparing Execution Plans
Query Store also allows DBAs to compare execution plans for a specific query to analyze plan changes over time. Follow these steps to compare execution plans:
1. Open SSMS, connect to your SQL Server instance, and expand the target database.
2. Navigate to the “Query Store” node and expand it to reveal the “Queries” sub-node.
3. Right-click on the “Queries” sub-node and select “Query Text”.
4. In the “Query Text” dialog, enter the SQL query for which you want to compare execution plans and click “OK”.
5. You will see a list of available execution plans for the specified query. Select the plans you want to compare and click “Compare” at the bottom of the dialog.
6. The execution plans will be displayed side by side, providing insights into plan changes, including differences in estimated and actual execution counts, operator costs, and more.
Monitoring Query Performance Over Time
Query Store provides an extensive set of built-in reports that allow DBAs to monitor query performance trends over time. These reports present visual representations of data captured by Query Store and help in identifying long-term performance patterns. Here are the steps to access Query Store reports:
1. Open SSMS, connect to your SQL Server instance, and expand the target database.
2. Right-click on the target database and select “Reports” -> “Standard Reports” -> “Performance – Query Statistics”.
3. SSMS will open a new window with the Query Store Performance Dashboard report. This report provides an overview of query performance, including top queries, plan regressions, and execution statistics.
4. You can customize the report by applying filters, changing time intervals, and selecting specific queries or plans.
Troubleshooting Query Performance using Query Store
Apart from performance analysis, Query Store also helps in troubleshooting query-related issues. Let’s explore how Query Store empowers DBAs in this regard.
Identifying Query Regressions
Query regressions occur when the performance of a query degrades over time. Query Store makes it easier to identify such regressions by comparing performance metrics of a query across different time intervals. Follow these steps:
1. Open SSMS, connect to your SQL Server instance, and expand the target database.
2. Navigate to the “Query Store” node and expand it to reveal the “Queries” sub-node.
3. Right-click on the “Queries” sub-node and select “Top Resource Consuming Queries”.
4. In the “Top Resource Consuming Queries” dialog, select the query you suspect has regressed and click “OK”.
5. The report will show performance metrics for the selected query over different time periods, helping you identify any regressions.
Forcing Query Plans
In some cases, the SQL Server query optimizer may choose suboptimal execution plans for certain queries. Query Store allows you to force a specific plan for a query to improve performance. Here’s how you can force a query plan:
1. Open SSMS, connect to your SQL Server instance, and expand the target database.
2. Navigate to the “Query Store” node and expand it to reveal the “Queries” sub-node.
3. Right-click on the “Queries” sub-node and select “Query Text”.
4. In the “Query Text” dialog, enter the SQL query for which you want to force a plan.
5. Select the desired plan from the list of available plans and click “Force Plan” at the bottom of the dialog.
6. SQL Server will now use the forced plan for the specified query, potentially improving performance.
FAQs
Q: Can I use Query Store with previous versions of SQL Server?
A: No, Query Store is available starting from SQL Server 2016.
Q: Is enabling Query Store resource-intensive?
A: Enabling Query Store has a minimal performance impact. However, you should monitor resource usage and adjust configuration options accordingly.
Q: How long does Query Store retain captured data?
A: The retention period is determined by the “Data Flush Interval (Minutes)” configuration option. By default, data is retained for 30 days.
Q: Can I force a plan for all executions of a query?
A: Yes, you can force a plan for a query using the “Force Plan” feature. However, be cautious when using this option, as it can have unintended consequences.
Q: Can I disable Query Store after enabling it?
A: Yes, you can disable Query Store for a database. However, keep in mind that disabling Query Store will result in the loss of all captured data.
Q: Can I use the Query Store on Azure SQL Database?
A: Yes, Query Store is available on Azure SQL Database as well as Azure SQL Managed Instance.
Conclusion
The SQL Server Query Store is a powerful tool that enables DBAs to monitor and troubleshoot query performance. By leveraging its features such as capturing query details, comparing execution plans, and monitoring performance over time, DBAs can efficiently analyze and resolve query-related issues. With the step-by-step approach outlined in this guide, you can demystify the SQL Server Query Store and unlock its full potential for performance analysis and troubleshooting.
