How can you use SQL Server’s Query Store feature to monitor and troubleshoot query performance?

SQL Server’s Query Store is a powerful feature that can be used to monitor and troubleshoot query performance. It provides a way to capture and store query performance data (such as execution plans, run-time statistics, and execution history) over time, which can be used to identify and troubleshoot performance issues.

Here are some steps to using Query Store to monitor and troubleshoot query performance:

1. Enable Query Store - To enable Query Store for a database, simply execute the following command:

ALTER DATABASE [database_name] SET QUERY_STORE = ON;

2. Configure Query Store settings - Configure Query Store to collect the necessary data to monitor query performance by setting options like data retention (how long to store data), capture mode (to capture all queries or only those that cause performance issues), and query store size.

3. Monitor query performance - Query Store provides several built-in reports that you can use to monitor query performance, such as the Top Resource-Consuming Queries report, the Regressed Queries report, and the Query Store Overall Resource Consumption report. These reports can be accessed via SQL Server Management Studio (SSMS) or by using T-SQL queries.

4. Troubleshoot performance issues - Query Store allows troubleshooting of performance issues by identifying queries that are consuming a high amount of resources. The built-in reports available in Query Store can be used to identify queries with high average CPU usage, high average duration, or high IO usage, which can then be further analyzed to identify performance issues.

5. Analyze query execution plans - Query Store provides a way to view the execution plans of the queries that were executed in the past, which can be used to identify issues like plan changes or plan regressions that are causing performance issues.

For example, here’s a T-SQL query that can be used to identify the top 10 resource-consuming queries in Query Store:

SELECT TOP 10
  qt.query_sql_text,
  qsp.*
FROM 
  sys.query_store_query_text AS qt
  JOIN sys.query_store_plan AS qsp ON qt.query_text_id = qsp.query_text_id
ORDER BY 
  qsp.cpu_time DESC;

Overall, Query Store is a powerful tool that can be used by SQL Server Database expert to monitor and troubleshoot query performance issues, aiding them in identifying and resolving issues that may be detrimental system’s overall performance.