如何从SQL Server内存中清除SqlDependency？

Question

如何清理SQL Server以清除过期的SqlDependency对象？从SqlDepedency对象收到事件后,我需要创建一个新事件才能获得新事件.但是,SQL Server进程的内存使用量会增加,直到超出允许的内存(SQL Server Express).如何摆脱旧查询？

码:

// Func: RegisterTableListener
using (SqlConnection cn = new SqlConnection(Properties.Settings.Default.DatabseEventConnectionString))
{
if (cmd == null)
{
    cmd = cn.CreateCommand();

    cmd.CommandType = CommandType.Text;
    cmd.CommandText = "SELECT HostName, LastStatus, LastDetails, xml FROM dbo.[SystemTable]";
}

lock (cmd)
{
    cmd.Connection = cn;
    cn.Open();
    cmd.Notification = null;

    //  creates a new dependency for the SqlCommand
    if (dep == null)
        dep = new SqlDependency(cmd);
    //  creates an event handler for the notification of data
    //      changes in the database.
    dep.OnChange += new OnChangeEventHandler(dependency_OnChange);


    using (SqlDataReader reader = cmd.ExecuteReader())
    {
    // code here to read
    }
}
}

// Func dependency_OnChange
//SqlDependency dep = sender as SqlDependency;
dep.OnChange -= dependency_OnChange;
RegisterTableListener();

Answer 1

Microsoft SqlDependency类有一个特定的行为.即使您调用SqlDependency.Stop()方法,释放SqlCommand和SqlConnection - 它仍然保留数据库中的会话组(sys.conversation_groups)和会话端点(sys.conversation_endpoints).看起来SQL Server加载每个会话端点并使用所有允许的内存.这里测试证明了这一点.因此,要清除所有未使用的会话端点并释放所有占用的内存,您必须为数据库启动此SQL代码:

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;

此外,SqlDependency不会让您有机会接收表的所有更改.因此,在SqlDependency重新订阅期间,您不会收到有关更改的通知.

为了避免所有这些问题,我使用了另一个SqlDependency类的开源实现--SqlDependencyEx.它使用数据库触发器和本机Service Broker通知来接收有关表更改的事件.这是一个用法示例:

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);

希望这可以帮助.