Mastering Query Store for SQL Server Performance Troubleshooting: A Step-by-Step Guide
Tags: sqlserver, postgres
Published: 2024-02-05 18:58:17

Using Query Store for troubleshooting SQL Server performance involves several steps, from enabling Query Store on your database to analyzing and acting on the data it collects. Here's a structured approach to leveraging Query Store for performance troubleshooting:

### Step 1: Enabling Query Store

First, you need to ensure Query Store is enabled for your database. This can be done via SQL Server Management Studio (SSMS) or by executing a T-SQL command:

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

```

You can also configure various settings such as data capture mode, data retention settings, and storage size limits. For example, to set the operation mode to capture all queries and configure the maximum storage size to 1 GB, you can use:

```sql
ALTER DATABASE [YourDatabaseName] SET QUERY_STORE (OPERATION_MODE = READ_WRITE, MAX_STORAGE_SIZE_MB = 1024);

```

### Step 2: Configuring Query Store Settings

Adjust Query Store settings based on your performance troubleshooting needs. Important settings include:

- **Data Flush Interval**: Determines how frequently collected data is written to disk.
- **Statistics Collection Interval**: Affects the granularity of performance data.
- **Max Size (MB)**: Sets the maximum amount of storage space Query Store can use.
- **Query Capture Mode**: Controls which queries are captured (all, auto, or none).

These settings can be configured through SSMS under the database properties window or via T-SQL commands.

### Step 3: Identifying Problematic Queries

Once Query Store is collecting data, you can start identifying problematic queries using the built-in reports in SSMS:

- **Overall Resource Consumption**: Shows the top queries consuming the most resources.
- **Top Resource Consuming Queries**: Identifies queries that have used the most CPU, I/O, or memory.
- **Queries with High Variation**: Helps find queries whose performance is inconsistent.
- **Tracked Queries**: Allows you to monitor specific queries over time.

To access these reports, right-click on the database in SSMS, navigate to Reports → Standard Reports, and then select the desired Query Store report.

### Step 4: Analyzing Query Performance

For each identified problematic query, analyze its performance by reviewing:

- **Execution Plans**: Compare historical execution plans to identify changes that may have led to performance degradation.
- **Runtime Statistics**: Look at metrics like execution time, logical reads, and CPU usage to understand the performance impact.

### Step 5: Forcing Plans

If you identify a specific execution plan that performs better than the current plan, Query Store allows you to force SQL Server to use that plan for future executions:

```sql
EXEC sp_query_store_force_plan @query_id = YourQueryID, @plan_id = YourPlanID;

```

This should be done cautiously, as forcing plans can have unintended consequences if not properly tested.

### Step 6: Monitoring and Adjusting

After making changes, continue to monitor the performance of the affected queries and the overall health of your SQL Server instance. If the forced plans do not yield the expected improvements or cause other issues, they can be unforced using:

```sql
EXEC sp_query_store_unforce_plan @query_id = YourQueryID, @plan_id = YourPlanID;

```

### Step 7: Regular Maintenance

Regularly review Query Store settings and the data it contains to ensure it's operating efficiently. This includes:

- Checking the storage space used by Query Store.
- Adjusting retention settings as needed to balance performance data granularity with storage limitations.
- Periodically clearing old or irrelevant data to keep Query Store manageable and focused on current performance issues.

Query Store is a powerful feature for identifying and resolving SQL Server performance issues, but it requires ongoing management and analysis to fully leverage its capabilities. By following these steps, you can effectively use Query Store to troubleshoot and improve the performance of your SQL Server databases.

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