How to Clean Up Expired SqlDependency Objects and Prevent SQL Server Memory Leaks?

Addressing SQL Server Memory Leaks Caused by Expired SqlDependency Objects

The Problem:

SQL Server's memory usage can steadily increase when using SqlDependency objects. This is because, even after calling SqlDependency.Stop() and releasing the SqlCommand and SqlConnection, the database retains conversation groups and endpoints. This accumulation eventually leads to memory exhaustion, especially in SQL Server Express.

The Solution:

The following SQL script cleans up these expired conversation endpoints:

<code class="language-sql">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;</code>

Execute this script against the database experiencing the memory leak.

SqlDependency Limitations:

It's important to understand that SqlDependency isn't perfect. It may miss some table changes, particularly those occurring during its resubscription process.

A Better Approach: SqlDependencyEx

For a more robust and reliable solution, consider using SqlDependencyEx, an open-source alternative. It leverages database triggers and Service Broker notifications for more effective change event handling. Here's an example:

<code class="language-csharp">int changesReceived = 0;
using (SqlDependencyEx sqlDependency = new SqlDependencyEx(
          TEST_CONNECTION_STRING, TEST_DATABASE_NAME, TEST_TABLE_NAME)) 
{
    sqlDependency.TableChanged += (o, e) => changesReceived++;
    sqlDependency.Start();

    // Make table changes.
    MakeTableInsertDeleteChanges(changesCount);

    // Wait a little bit to receive all changes.
    Thread.Sleep(1000);
}

Assert.AreEqual(changesCount, changesReceived);</code>

SqlDependencyEx provides superior change tracking and eliminates the memory issues associated with the standard SqlDependency.

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