SaveChanges()不是由事务管理的吗?

我有几个“线程”(即Hangfire任务)将并行运行这种函数(每个调用传递不同的 systemId ):

private void UpdatePartners(int systemId)
{
    try
    {
        using (var ctx = new MyEntities())
        {
            var partners = ctx.PartnersUpdate.Select(s => s)
              .Where(w => w.SystemId.Equals(systemId) && statusToEvaluate.Contains(w.Status)).OrderByDescending(p => p.UpdateAt).Take(500);

            var partnersId = partners.Select(p => p.PartnerId).ToList();

            var partnersToUpdate = ctx.vPartnersSystems.AsNoTracking().Select(s => s)
                    .Where(w => w.SystemId.Equals(systemId) && partnersId.Contains(w.Id) && w.Validity.Equals(true))
                    .ToList();

            foreach (var partner in partners)
            {
                // some operations on "partner", using data from "partnersToUpdate"
                
                ctx.PartnersUpdate.AddOrUpdate(partner);
            }

            ctx.SaveChanges();
        }
    }
    catch (Exception ex)
    {
        Logger(ex, "Error on UpdatePartners");
    }
}

不幸的是,有时我会遇到这个错误:

UpdatePartners(Int32 systemId) in C:\myProjects\XYZ\Controllers\TestController.cs:line 16 Void HandleReaderException(System.Exception)
System.Data.SqlClient.SqlException (0x80131904): Transaction (Process ID 130) was deadlocked on lock | communication buffer resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

当迭代合作伙伴时(但我可能错了):

foreach (var partner in partners)

为什么?如果 UpdatePartners() 与不同的并行调用 系统ID (这意味着每次查询都会捕获 不同的记录 ),为什么它处理“死锁”?

“相同行”的死锁不是被读取/更新了吗?