In a database management system, query waits can have a significant impact on overall performance. Understanding and analyzing query wait statistics is crucial for identifying and resolving performance bottlenecks. Fortunately, with the SQL Query Store, you can easily track and analyze query waits to optimize your database performance.

What are Query Waits?

Query waits refer to the amount of time a query spends waiting for a particular resource or event to occur. It is an indication of the query’s performance against different resources like locks, disk I/O, memory, and network latency. Query waits can be categorized into various types, such as lock waits, disk I/O waits, and network waits.

Introducing the SQL Query Store

The SQL Query Store is a powerful feature introduced in Microsoft SQL Server 2016 and later versions. It provides a built-in mechanism to capture and analyze query performance data. With the Query Store, you can easily monitor and troubleshoot query performance issues.

Tracking Query Waits with the SQL Query Store

The SQL Query Store captures a wide range of performance data, including query waits. To track query waits using the Query Store, follow these steps:

1. Enable the Query Store on your database:

   ALTER DATABASE [YourDatabaseName] SET QUERY_STORE = ON;
   

2. Configure the Query Store settings, such as capture mode and data retention period:

   ALTER DATABASE [YourDatabaseName] SET QUERY_STORE (OPERATION_MODE = READ_WRITE, CLEANUP_POLICY = (STALE_QUERY_THRESHOLD_DAYS = 30));
   

3. Query the sys.query_store_wait_stats view to get the query wait statistics:

   SELECT * FROM sys.query_store_wait_stats;
   

The sys.query_store_wait_stats view provides detailed information about various query waits, including wait type, total wait time, and total waits.

Analyzing Query Wait Statistics

Once you have gathered the query wait statistics using the SQL Query Store, you can analyze the data to identify potential performance issues. Here are some techniques for analyzing query wait statistics:

1. Identify the top wait types:

   SELECT TOP (10) * FROM sys.query_store_wait_stats ORDER BY total_wait_time_ms DESC;
   

   This query will give you the top 10 wait types with the highest total wait time.

2. Dig deeper into specific wait types:

   SELECT * FROM sys.query_store_wait_stats WHERE wait_type = 'PAGEIOLATCH_SH';
   

   Replace “PAGEIOLATCH_SH” with the specific wait type you want to investigate. This query will provide detailed information about queries experiencing this particular wait type.

3. Compare wait statistics over time:

   SELECT * FROM sys.query_store_wait_stats where start_time between '2022-01-01 00:00:00' and '2022-01-31 23:59:59';
   

   Adjust the date range to compare query wait statistics over a specific period. This query can help you identify trends and patterns in wait times.

4. Utilize graphical reports: The SQL Server Management Studio (SSMS) provides graphical reports for analyzing query wait statistics. Right-click on your database, select “Reports,” and choose the “Query Store” section. From there, you can explore different reports, including “Top Resource Waits” and “Wait Statistics by Query Text.”

Conclusion

Analyzing query wait statistics is essential for diagnosing and improving database performance. With the SQL Query Store, you have a powerful tool at your disposal to track and analyze query waits. By identifying and addressing the root causes of query waits, you can optimize your database performance and enhance overall application responsiveness.

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