How Can I Clean Up Expired SqlDependency Objects to Free SQL Server Memory?

Clearing Out Unused SqlDependency Objects in SQL Server to Free Up Memory

SQL Server's memory management can be impacted by a build-up of expired SqlDependency objects, leading to high memory consumption by the SQL Server process. This can severely impact performance, particularly in SQL Server Express, potentially causing memory exhaustion and application crashes.

Addressing the Issue

The core problem lies in how Microsoft's SqlDependency functions. Even after calling SqlDependency.Stop() and releasing references to SqlCommand and SqlConnection, associated conversation groups and endpoints persist in the database, continuing to consume memory.

Cleanup Steps

To remove these unused conversation endpoints and free up memory, execute this SQL script against your database:

-- Disable conversation groups without index to prepare for endpoint deletion
ALTER DATABASE <database_name> SET ALLOW_CONVERSATIONS_WITHOUT_INDEX = OFF;
GO

-- Remove disconnected conversation endpoints
DELETE CEP
FROM sys.conversation_endpoints CEP
WHERE CEP.state = 'DI' OR CEP.state = 'CD';
GO

-- Re-enable conversation groups
ALTER DATABASE <database_name> SET ALLOW_CONVERSATIONS_WITHOUT_INDEX = ON;
GO

SqlDependency Limitations

It's important to note that SqlDependency has limitations. It doesn't always detect all table changes, especially when resubscribing.

A Better Approach: SqlDependencyEx

For more robust change tracking, consider the open-source alternative, SqlDependencyEx. This library uses database triggers and Service Broker notifications for more reliable monitoring of table modifications. Here's an example:

int changesReceived = 0;
using (SqlDependencyEx sqlDependency = new SqlDependencyEx(
          TEST_CONNECTION_STRING, TEST_DATABASE_NAME, TEST_TABLE_NAME)) 
{
    sqlDependency.TableChanged += (o, e) => changesReceived++;
    sqlDependency.Start();

    // Simulate table changes
    MakeTableInsertDeleteChanges(changesCount);

    // Allow time for changes to be processed
    Thread.Sleep(1000);
}

Assert.AreEqual(changesCount, changesReceived);

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