An Introduction to SQL Server Query Store
Tags: sql
Published: 2024-04-01 12:58:48

In the world of database management, maintaining optimal performance is a continual challenge. Database administrators and developers constantly seek tools and methodologies to monitor, troubleshoot, and optimize database operations. Introduced in SQL Server 2016, the Query Store feature has emerged as a game-changer, offering a rich set of capabilities to address these needs. This article delves into the SQL Server Query Store, guiding you through enabling, configuring, and utilizing this feature to enhance your database's performance.

## What is SQL Server Query Store?

The SQL Server Query Store functions as a "flight recorder" for your database, capturing detailed information about query execution, including execution statistics, query texts, and execution plans. This treasure trove of data opens up new vistas for performance monitoring and tuning, enabling database professionals to diagnose issues and improve query performance with unprecedented precision.

## Enabling Query Store

By default, the Query Store is turned off. To leverage its capabilities, you first need to enable it for your database. This can be done effortlessly with a T-SQL command:

```sql
ALTER DATABASE [YourDatabaseName] SET QUERY_STORE = ON;
```

Just replace `[YourDatabaseName]` with the name of your target database. This simple action activates the Query Store, setting the stage for a more performant database by allowing you to collect and analyze query performance data.

## Configuring Query Store Settings

The Query Store comes with a variety of settings that you can configure to suit your monitoring and performance tuning strategies. These settings include data flush intervals, storage size limits, and data retention policies. For instance, you can adjust the Query Store's settings with the following T-SQL command:

```sql
ALTER DATABASE [YourDatabaseName] 
SET QUERY_STORE (OPERATION_MODE = READ_WRITE, 
                 CLEANUP_POLICY = (STALE_QUERY_THRESHOLD_DAYS = 30), 
                 DATA_FLUSH_INTERVAL_SECONDS = 900, 
                 MAX_STORAGE_SIZE_MB = 1000);
```

These settings enable the Query Store, set it to read/write mode, specify that queries not executed in the last 30 days should be removed, set the data flush interval to 15 minutes, and limit the Query Store's maximum data size to 1GB.

## Querying the Query Store

With the Query Store enabled and configured, it starts collecting data on executed queries. After giving it some time to gather data, you can begin querying the Query Store to extract valuable insights into your database's performance. For example, to identify the top 10 most resource-intensive queries, you can use:

```sql
SELECT TOP 10 
    qs.query_id, 
    q.text AS query_text, 
    qs.total_cpu_time_ms, 
    qs.total_execution_count
FROM sys.query_store_query qs
JOIN sys.query_store_query_text q ON qs.query_text_id = q.query_text_id
ORDER BY qs.total_cpu_time_ms DESC;
```

This query helps pinpoint the queries that are most taxing on your system, providing a starting point for optimization efforts.

## Leveraging Query Store for Performance Optimization

The Query Store's real power lies in its ability to track query performance over time, enabling DBAs and developers to:
- Identify and analyze slow-running or resource-intensive queries.
- Compare the performance of different query execution plans.
- Monitor the impact of changes to the database or queries.

Armed with this information, you can make informed decisions to optimize query performance, whether through index adjustments, query rewriting, or other tuning techniques.

## Conclusion

The SQL Server Query Store is an indispensable tool for anyone looking to enhance their database's performance. By providing detailed insights into query execution and performance, it empowers database professionals to identify bottlenecks, test optimizations, and ensure the stability and efficiency of their databases. Begin exploring the capabilities of the Query Store today, and take the first step towards a more performant and reliable database environment.

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