Batch execution mode is a powerful optimization feature in SQL Server that can significantly improve query performance. In this article, we will delve into how batch execution mode works and how you can leverage it to achieve faster query results on rowstore data.

Prerequisites for Enabling Batch Execution Mode

Before you can take advantage of batch execution mode, there are a few prerequisites to consider:

• Compatibility Level: Batch execution mode requires a compatibility level of at least 150. Make sure to check your database compatibility level before enabling this feature.
• Hardware: Batch execution mode requires a certain amount of memory and CPU resources. Ensure that your hardware is capable of handling the additional workload before enabling the feature.
• Rowstore Table: Batch execution mode only works on rowstore tables. Verify that your query is applicable to rowstore tables.

Enabling Batch Execution Mode

To enable batch execution mode, you need to perform the following steps:

1. Check that your compatibility level is set to at least 150.
2. Ensure that your query is written for rowstore tables only.
3. Verify that your hardware can handle the additional memory and CPU utilization.
4. Execute the following query to enable batch mode on rowstore:

ALTER DATABASE SCOPED CONFIGURATION SET BATCH_MODE_ON_ROWSTORE = ON;

You can disable batch mode on rowstore by executing the following query:

ALTER DATABASE SCOPED CONFIGURATION SET BATCH_MODE_ON_ROWSTORE = OFF;

Additionally, you can disable batch mode on rowstore for a specific query by using the DISALLOW_BATCH_MODE query hint.

The Benefits of Batch Execution Mode

Batch execution mode offers several benefits:

• Optimized Memory Usage: Batch execution mode reduces memory usage and lowers the required memory grants for queries. This results in faster and more efficient processing of larger queries.
• Improved Query Performance: Batch execution mode processes multiple rows at once, leading to improved query performance. This means faster and more accurate results with reduced waiting time.
• Better CPU Utilization: Batch execution mode efficiently utilizes the CPU, potentially reducing the overall CPU time per query by up to 50% in certain cases.

Let’s illustrate the impact of batch execution mode with an example. Consider the following query:

SELECT [SalesOrderID], SUM([OrderQty]*[ProductID]) AS sale, [ModifiedDate]
FROM [Sales].[SalesOrderDetail]

When executed with a database compatibility level of 140, the query runs in row execution mode. However, after setting the compatibility level to 160 and resetting the caches, the query switches to batch execution mode. This change results in a significant reduction in CPU time, showcasing the performance improvement.

Limitations and Restrictions

While batch execution mode offers substantial benefits, there are a few limitations to be aware of:

• Batch Execution Mode Complexity: Batch execution mode is only supported on simple queries that do not require index intersection, hash join, or many subqueries.
• Data Types: Batch execution mode only supports certain data types and conversions. Ensure that your query aligns with the supported data types to maximize performance.
• Resources: Batch execution mode may require additional resources such as memory and CPU. Make sure your system can handle the increased workload before enabling this feature.

It is crucial to understand these limitations and restrictions before enabling batch execution mode. While these restrictions do not apply to all queries, it is recommended to thoroughly test the feature before implementing it in a production environment.

Best Practices for Optimizing Batch Execution Mode

To optimize batch execution mode, consider the following best practices:

• Utilize Columnstore Indexes: Columnstore indexes work exceptionally well with batch execution mode due to their ability to process large amounts of data quickly.
• Minimize Data Conversion: Since batch execution mode is designed to work with specific data types, minimize the number of data conversions in your query to increase performance and reduce resource usage.
• Use Proper Query Design: Batch execution mode is most effective in queries without many joins or subqueries. Optimize your queries for performance before enabling batch execution mode.

Conclusion

Batch execution mode can be a game-changer in terms of query performance when used with rowstore data. By following the best practices and considerations outlined in this article, you can ensure that your queries are maximizing the potential benefits of batch execution mode. Test thoroughly and enable with confidence, knowing that you’re on your way to lightning-fast query results.