I use JMeter to test my web application. and my test case is to add a record in database. and then I set the "number of thread user" to 20, it means that it will simulate 20 users work at the same time. and then I run the test case. But finally i found the system didn t create 20 records in database, but instead just create 13 records in database.

I want to know why this happened ? Is it possible that because in my web application i didn t add a "synchronized" in front of the add records method ? I used linq, If two user post a request to create a record to server at the same time, what will happen? Just create a record or can successfully create two records, or unknown ?

Following is the sample code for create a record in database:

       public int SaveEventGroup(int id, Models.Entities.EventGroup e, Nullable<int> setpublish)
    {
        try
        {
            Entities.EventGroup db;
            if (id == 0)
            {
                db = new Entities.EventGroup();
                db.CreatedBy = e.CreatedBy;
                db.CreateDatetime = DateTime.Now;
                db.Status = true;
            }
            else
            {
                db = this.GetEventGroup(id);
            }

            db.NameCN = e.NameCN;
            db.NameEN = e.NameEN;
            db.NameZH = e.NameZH;
            db.NamePT = e.NamePT;
            db.DisplayOrder = GetGroupMaxDisplayOrder() + 1;

            if (setpublish == null)
            {
                db.PublishStatus = false;
                db.PublishDatetime = null;
                db.UpdateDatetime = DateTime.Now;
                db.UpdatedBy = e.UpdatedBy;
            }

            if (id == 0)
                dataContext.AddToEventGroupSet(db);

            dataContext.SaveChanges();

            return db.Id;
        }
        catch (Exception ex)
        {
            log.Error(ex.Message, ex);
            throw ex;
        }
    }