How to Resolve SQL Server Memory Leaks Caused by Expired SqlDependency Objects?

Addressing SQL Server Memory Leaks from Expired SqlDependency Objects

The Problem:

Applications utilizing the SqlDependency class for SQL Server database change monitoring can experience memory leaks. Expired SqlDependency objects accumulate in memory, potentially exhausting system resources.

Root Cause:

SqlDependency establishes a server connection and registers table notifications. Even after dependency removal or resource release (SqlCommand, SqlConnection), associated conversation groups and endpoints persist in the database, consuming memory.

Solution: Database Cleanup

To reclaim memory occupied by expired SqlDependency objects, execute this SQL script within the affected database:

<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>

SqlDependency Limitations:

Beyond memory management, SqlDependency has inherent limitations:

• Inconsistent change notification: Not all table modifications trigger notifications.
• Resubscription gap: Changes during resubscription are not reported.

Alternative: SqlDependencyEx Library

For improved reliability and comprehensive change tracking, consider the open-source SqlDependencyEx library. It uses database triggers and Service Broker for more robust notification:

<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();

    // Simulate table changes.
    MakeTableInsertDeleteChanges(changesCount);

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

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

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