Batch Mode Processing in SQL Server

 Batch Mode Processing in SQL Server is an optimization technique primarily used for processing large sets of data efficiently, especially in analytical workloads. It was introduced with columnstore indexes in SQL Server 2012 and has been extended and improved in subsequent versions. Batch mode processing operates on batches of rows, typically 900 rows at a time, rather than processing one row at a time. This can result in significant performance improvements for certain types of queries.

Key Concepts

• Columnstore Indexes: Batch mode processing was initially tied to columnstore indexes. Columnstore indexes store data in a columnar format, which is highly efficient for analytical queries.
• Batch Mode on Rowstore: Starting with SQL Server 2019, batch mode processing is also available on rowstore indexes, which means you can benefit from batch mode processing without using columnstore indexes.

Benefits

• Improved CPU Utilization: Batch mode processing can reduce CPU cycles needed for query execution.
• Memory Efficiency: Better memory utilization due to operating on batches of rows.
• Parallelism: Enhanced parallelism leading to faster query execution times.

Example: Using Batch Mode Processing with Columnstore Indexes

Step 1: Create a Table and Insert Data

First, create a table and insert a large amount of data into it.

USE YourDatabase; -- Replace with your database name
GO

-- Create a sample table
CREATE TABLE Sales (
    SaleID INT IDENTITY(1,1),
    ProductID INT,
    CustomerID INT,
    SaleDate DATE,
    SaleAmount DECIMAL(10, 2)
);
GO

-- Insert sample data
INSERT INTO Sales (ProductID, CustomerID, SaleDate, SaleAmount)
SELECT TOP (1000000)
    ABS(CHECKSUM(NEWID())) % 1000,
    ABS(CHECKSUM(NEWID())) % 1000,
    DATEADD(DAY, ABS(CHECKSUM(NEWID())) % 365, '2020-01-01'),
    ABS(CHECKSUM(NEWID())) % 1000 + 0.99
FROM sys.objects s1
CROSS JOIN sys.objects s2;
GO

Step 2: Create a Columnstore Index

Next, create a columnstore index on the table to enable batch mode processing.

-- Create a clustered columnstore index
CREATE CLUSTERED COLUMNSTORE INDEX CCI_Sales ON Sales;
GO

Step 3: Run a Query and Observe the Execution Plan

Run an analytical query and observe the execution plan to see if batch mode processing is being used.

-- Run a sample query
SELECT
    ProductID,
    COUNT(*) AS TotalSales,
    SUM(SaleAmount) AS TotalAmount
FROM Sales
GROUP BY ProductID;
GO

-- View the execution plan
-- (In SSMS, enable "Include Actual Execution Plan" before running the query)

In the execution plan, look for operators that indicate batch mode processing, such as "Columnstore Index Scan" or "Batch Hash Table Build".

Using Batch Mode on Rowstore

In SQL Server 2019 and later, batch mode processing can be used on rowstore tables, which means you don't necessarily need a columnstore index to benefit from batch mode.

Step 1: Enable Compatibility Level

Ensure your database is set to a compatibility level that supports batch mode on rowstore (SQL Server 2019 or later).

ALTER DATABASE YourDatabase SET COMPATIBILITY_LEVEL = 150;
GO

Step 2: Create a Rowstore Table and Insert Data

Create a rowstore table and insert data.

-- Create a sample rowstore table
CREATE TABLE SalesRowstore (
    SaleID INT IDENTITY(1,1),
    ProductID INT,
    CustomerID INT,
    SaleDate DATE,
    SaleAmount DECIMAL(10, 2)
);
GO

-- Insert sample data
INSERT INTO SalesRowstore (ProductID, CustomerID, SaleDate, SaleAmount)
SELECT TOP (1000000)
    ABS(CHECKSUM(NEWID())) % 1000,
    ABS(CHECKSUM(NEWID())) % 1000,
    DATEADD(DAY, ABS(CHECKSUM(NEWID())) % 365, '2020-01-01'),
    ABS(CHECKSUM(NEWID())) % 1000 + 0.99
FROM sys.objects s1
CROSS JOIN sys.objects s2;
GO

Step 3: Run a Query and Observe the Execution Plan

Run an analytical query and observe the execution plan to see if batch mode processing is being used.

-- Run a sample query
SELECT
    ProductID,
    COUNT(*) AS TotalSales,
    SUM(SaleAmount) AS TotalAmount
FROM SalesRowstore
GROUP BY ProductID;
GO

-- View the execution plan
-- (In SSMS, enable "Include Actual Execution Plan" before running the query)

Look for "Batch Mode" indicators in the execution plan, such as "Batch Hash Table Build".

Conclusion

Batch mode processing can significantly improve the performance of large-scale analytical queries by processing rows in batches. Initially tied to columnstore indexes, batch mode processing has been extended to rowstore tables in SQL Server 2019, making it accessible to a broader range of queries and workloads. By leveraging this feature, you can optimize your SQL Server for better performance in data-intensive operations.