Hi,

I get StackOverflowException with code like this:

internal class Program
{
    public const int IterationsCount = 50000;

    private static void Main(string[] args)
    {
        var dc = new DomainConfiguration("sqlserver", "Data Source=.; Initial Catalog=DO40-Tests; Integrated Security=True;")
        {
            UpgradeMode = DomainUpgradeMode.Recreate,
        };

        dc.Types.Register(typeof(Program).Assembly);

        var sw = new Stopwatch();

        using (var d = Domain.Build(dc))
        {    
            using (var s = d.OpenSession(SessionConfiguration.Default))
            using (s.Activate())
            using (var t1 = s.OpenTransaction(TransactionOpenMode.New))
            {
                sw.Start();

                var ent = new Ent();

                for (var i = 0; i < IterationsCount; i++)
                {
                    Session.Current.Query.All<Ent>().Where(z => z.Id == ent.Id).ToArray();

                    ent.Num = i;

                    if (i % 10 == 0)
                    {
                        Console.WriteLine($"{i}    {sw.Elapsed.TotalSeconds}");
                        sw.Restart();
                    }
                }

                t1.Complete(); 
            }
        }
    }
}

   [HierarchyRoot]
   public class Ent : Entity
   {
       [Field, Key]
       public Guid Id { get; set; }

       [Field]
       public int Num { get; set; }
   }

Stacktrace shows that cause of StackOverflowException is recursive call of Xtensive.Tuples.DifferentialTuple.Clone() method.

Also before StackOverflow is thrown performance dramatically decrease

DO version: 5.0.13