In the realm of database management, optimizing performance while minimizing resource contention is a perennial challenge. One of the critical areas where contention can be notably reduced is in the utilization of temporary storage mechanisms like tempdb. SQL Server’s In-Memory OLTP feature offers a compelling solution to this challenge, particularly through the use of in-memory optimized table variables. This post explores how leveraging In-Memory OLTP table variables can significantly improve performance by alleviating tempdb allocation contention, especially when compared to traditional table variables, temporary tables, or common table expressions (CTEs).

Understanding tempdb Contention

Before diving into the solution, it’s crucial to understand the problem. The tempdb system database in SQL Server is a shared resource used for various temporary storage activities, including user-created temporary tables, temporary stored procedures, table variables, and CTEs. However, heavy tempdb usage, particularly in high-concurrency environments, can lead to contention issues, impacting overall database performance.

Enter In-Memory OLTP Table Variables

In-Memory OLTP, introduced in SQL Server 2014, revolutionized how data is stored and accessed by storing designated tables and table variables in memory rather than on disk. This feature not only speeds up data access but also significantly reduces contention by bypassing traditional disk-based storage mechanisms.

Defining an In-Memory OLTP Table Variable

Unlike regular table variables, an in-memory OLTP table variable is defined as a user-defined table type with the MEMORY_OPTIMIZED = ON option. Here’s how to create one:

CREATE TYPE JB_InMem_TableType AS TABLE (
    col1 INT,
    col2 DATETIME,
    col3 VARCHAR(255),
    INDEX IX_JB_InMem_TableType_Col1 NONCLUSTERED (Col1)
) WITH (MEMORY_OPTIMIZED = ON);
GO

Utilizing In-Memory OLTP Table Variables in Stored Procedures

In-memory OLTP table variables can be seamlessly integrated into stored procedures. Here’s a simple example:

CREATE PROCEDURE sp_proc1
    @Col1 INT
AS
BEGIN 
    DECLARE @jb_table1 JB_InMem_TableType;
    INSERT INTO @jb_table1 
    SELECT col1, col2, col3 FROM Table1
    SELECT col1, col2, col3 FROM @jb_table1 WHERE col1 = @Col1;
END
GO

In this example, @jb_table1 is populated from Table1 and then queried, all while residing entirely in memory.

Benefits Over Traditional Methods

The use of in-memory OLTP table variables offers several advantages over traditional table variables, temporary tables, or CTEs:

• Reduced tempdb Contention: Since in-memory objects do not rely on tempdb, they avoid contributing to tempdb contention, a common bottleneck in high-concurrency scenarios.
• Performance Improvement: Accessing data in memory is significantly faster than disk-based access, leading to improved query performance.
• Transactional Consistency: In-memory OLTP supports fully ACID-compliant transactions, ensuring data integrity without compromising on performance.

Conclusion

In-memory OLTP table variables represent a powerful tool in the SQL Server performance tuning arsenal. By leveraging in-memory storage, developers and DBAs can achieve significant performance improvements and reduce contention issues associated with tempdb. Whether you’re building high-performance applications or optimizing existing database workloads, the use of in-memory OLTP table variables is certainly worth considering.

Thank You,
Vivek Janakiraman

Disclaimer:
The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.