What is a Memory-Optimized Table Variable?
A Memory-Optimized Table Variable is a special type of table variable that uses SQL Server's In-Memory OLTP engine. Unlike regular table variables or temporary tables (#temp), it is stored in memory, reducing tempdb contention and boosting performance for workloads with frequent data manipulation.
Why is it Useful?
Memory-Optimized Table Variables provide.
- Faster performance: Avoids disk I/O by keeping data in memory.
- Tempdb contention reduction: Traditional temp tables and table variables rely on tempdb, which can be a bottleneck.
- Optimized latch-free concurrency: Uses memory-optimized data structures for ultra-fast access.
- Efficient for short-lived data: Ideal for scenarios where data exists only within a session or batch.
When to Use It?
You should use Memory-Optimized Table Variables when,
- Your queries experience tempdb contention.
- You perform frequent batch operations with temporary data.
- You need high-performance OLTP workloads with frequent inserts and lookups.
- You are working with stored procedures that rely on table variables.
Where to Use It?
- Stored procedures that process intermediate data.
- ETL workloads require temporary staging tables.
- High-performance transaction processing systems.
- Session-based data caching to avoid repeated database calls.
How to Use a Memory-Optimized Table Variable?
1. Enable Memory-Optimized Tables in the Database
Before using memory-optimized table variables, you must enable In-Memory OLTP.
ALTER DATABASE YourDatabase
ADD FILEGROUP MemoryOptimizedFG CONTAINS MEMORY_OPTIMIZED_DATA;
ALTER DATABASE YourDatabase
ADD FILE (NAME = 'MemOptData', FILENAME = 'C:\Data\MemOptData')
TO FILEGROUP MemoryOptimizedFG;
2. Declare a Memory-Optimized Table Variable
Unlike a regular table variable, you must use MEMORY_OPTIMIZED = ON.
DECLARE @MemOptTable TABLE
(
ID INT NOT NULL PRIMARY KEY NONCLUSTERED,
Name NVARCHAR(100) NOT NULL
) WITH (MEMORY_OPTIMIZED = ON);
3. Insert and Query Data Efficiently
INSERT INTO @MemOptTable (ID, Name) VALUES (1, 'SQL Server'), (2, 'DBA Expert');
SELECT * FROM @MemOptTable;
4. Compare with Traditional Table Variables
A traditional table variable.
DECLARE @TableVar TABLE (ID INT, Name NVARCHAR(100));
- Uses tempdb, causing I/O overhead.
- Suffers from locking and latching under high concurrency.
Memory-Optimized Table Variables
- Avoid tempdb entirely.
- Are lock-free and latch-free, making them 10x faster in some cases.
Real-Time Example: Improving Performance in a High-Traffic System
- Scenario: A banking application processes thousands of real-time transactions per second. Using traditional table variables slows down the system due to tempdb contention.
- Solution: By replacing standard table variables with Memory-Optimized Table Variables, the system eliminates tempdb bottlenecks, resulting in a 40% faster transaction processing time.
DECLARE @TransactionLog TABLE
(
TransactionID INT NOT NULL PRIMARY KEY NONCLUSTERED,
AccountID INT NOT NULL,
Amount DECIMAL(10,2) NOT NULL
) WITH (MEMORY_OPTIMIZED = ON);
Memory-optimized table Variables were introduced in SQL Server 2016 and are available in the following versions.
Compatible SQL Server Versions
- SQL Server 2016 (13.x)
- SQL Server 2017 (14.x)
- SQL Server 2019 (15.x)
- SQL Server 2022 (16.x)
Not Available In
SQL Server 2014 and earlier (Memory-optimized tables were introduced in 2014, but table variables were not supported as memory-optimized until 2016).
Best Practices & Recommendations
- Enable In-Memory OLTP before using Memory-Optimized Table Variables.
- Use them in stored procedures or batch processing scenarios for best performance.
- Avoid using them for large datasets due to memory limitations.
- Use Non-Clustered Indexes properly to avoid performance bottlenecks.
- Test with different workloads before applying in production environments.