How to Clean Up SQL Server Memory Used by Expired SqlDependency Objects?

Effective Memory Management for SQL Server's SqlDependency Objects

Efficiently managing memory usage of SqlDependency objects in SQL Server is crucial for preventing performance issues. This guide addresses the problem of lingering expired SqlDependency objects and offers solutions.

The Problem: Memory Leaks

Even after event handling and object recreation, SQL Server (especially Express edition) may continue consuming memory until exhaustion. This is because SqlDependency leaves behind conversation groups and endpoints, even when the associated objects are no longer active.

The Solution: SQL Script for Cleanup

Execute the following SQL script against the database to remove unused conversation endpoints and reclaim memory:

DECLARE @ConvHandle uniqueidentifier
DECLARE Conv CURSOR FOR
SELECT CEP.conversation_handle FROM sys.conversation_endpoints CEP
WHERE CEP.state = 'DI' or CEP.state = 'CD'
OPEN Conv;
FETCH NEXT FROM Conv INTO @ConvHandle;
WHILE (@@FETCH_STATUS = 0) BEGIN
    END CONVERSATION @ConvHandle WITH CLEANUP;
    FETCH NEXT FROM Conv INTO @ConvHandle;
END
CLOSE Conv;
DEALLOCATE Conv;

This script iterates through conversation endpoints in a disconnected or closing state and terminates them, releasing the associated memory.

SqlDependency Limitations

It's important to be aware of SqlDependency's limitations:

• Incomplete Change Detection: SqlDependency might miss some table changes, requiring resubscription which can lead to missed updates.

A Superior Alternative: SqlDependencyEx

For improved SqlDependency management and overcoming its limitations, consider using the open-source SqlDependencyEx library. This library uses database triggers and Service Broker notifications for more reliable event handling:

using (SqlDependencyEx sqlDependency = new SqlDependencyEx(
          TEST_CONNECTION_STRING, TEST_DATABASE_NAME, TEST_TABLE_NAME)) 
{
    sqlDependency.TableChanged += (o, e) => changesReceived++;
    sqlDependency.Start();

    // Perform table modifications.
    MakeTableInsertDeleteChanges(changesCount);

    // Allow time for change reception.
    Thread.Sleep(1000);
}

This example demonstrates how SqlDependencyEx simplifies event handling and provides a more robust solution for monitoring table changes.

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