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Alex Underwood
Senior Program Manager, SQL Server

Query Store Deep Dive: Unlocking Performance Insights

In modern database management, understanding and optimizing query performance is paramount. One of the most powerful tools available in SQL Server for achieving this is the Query Store. Introduced in SQL Server 2016, Query Store provides a history of query performance, regressions, and plan choices, enabling developers and DBAs to pinpoint and resolve performance bottlenecks efficiently.

What is Query Store?

Query Store automatically captures a history of queries, execution plans, and runtime statistics in your SQL Server database. It then makes this information accessible for analysis. By default, it is disabled, but once enabled, it begins to collect data without significant overhead.

Key Components of Query Store

  • Query Text: The actual SQL statement.
  • Execution Plans: The different plans used to execute a query over time.
  • Runtime Statistics: Metrics like CPU time, elapsed time, logical reads, and row counts.
  • Performance Regressions: Automated detection of performance degradations.

Enabling and Configuring Query Store

Enabling Query Store is straightforward. You can do it via SQL Server Management Studio (SSMS) or T-SQL:


ALTER DATABASE YourDatabaseName
SET QUERY_STORE = ON
(
    OPERATION_MODE = READ_WRITE,
    CLEANUP_POLICY = (STALE_QUERY_THRESHOLD_DAYS = 30),
    DATA_FLUSH_INTERVAL_SECONDS = 300,
    MAX_STORAGE_SIZE_MB = 100
);

The configuration options allow you to control how data is collected and retained, ensuring efficient use of resources.

Analyzing Query Performance with Query Store

SSMS provides a dedicated Query Store interface, accessible from your database's properties. This interface offers several reports:

  • Top Resource Consuming Queries: Identifies queries that consume the most CPU, duration, or logical reads.
  • Queries with Regressions: Highlights queries whose performance has recently worsened.
  • Overall Top Queries: A general overview of frequently executed or resource-intensive queries.
  • Query Plan Analysis: Allows you to compare different execution plans for the same query and understand why a plan might be suboptimal.

Forcing a Specific Query Plan

One of the most powerful features is the ability to force a specific, known-good query plan. If Query Store identifies that a recent query plan compilation has led to a performance regression, you can instruct SQL Server to always use a previous, better-performing plan. This is done using the sp_query_store_force_plan stored procedure.


EXEC sp_query_store_force_plan @query_id = 123, @plan_id = 456;

Best Practices and Considerations

  • Regularly review Query Store reports to proactively identify performance issues.
  • Understand the CLEANUP_POLICY to manage storage growth.
  • Use Query Store in conjunction with other performance tuning tools and techniques.
  • Ensure your database compatibility level is set to 130 or higher for full functionality.

Conclusion

Query Store is an indispensable tool for anyone managing SQL Server databases. Its ability to capture, store, and analyze query performance data provides deep insights that can significantly improve database performance and stability. By leveraging its features, you can move from reactive firefighting to proactive performance management.