c# - Chosen as the deadlock victim on simple Add() -> SaveChanges()

Question

This simple program

private static void Main(string[] args)
{
    Parallel.For(0, 1000000, InsertTestEntity);
}

private static void InsertTestEntity(int i)
{
    using (var dbContext = new TestDbContext())
    {
        dbContext.TestEntities.Add(new TestEntity { HugeString = "Baby shark," + string.Join(", ", Enumerable.Repeat("doo", 500)) });
        dbContext.SaveChanges();
    }
}

public class TestEntity
{
    [Key]
    public int Id { get; set; }

    public string HugeString { get; set; }
}

public class TestDbContext : DbContext
{
    public DbSet<TestEntity> TestEntities { get; set; }
}

Throws an exception like

System.Data.Entity.Infrastructure.DbUpdateException
  HResult=0x80131501
  Message=An error occurred while updating the entries. See the inner exception for details.
  Source=EntityFramework
  StackTrace:
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at EntityFrameworkStressTest.Program.InsertTestEntity(Int32 i) in c:GitEntityFrameworkStressTestEntityFrameworkStressTestProgram.cs:line 18
   at System.Threading.Tasks.Parallel.<>c__DisplayClass17_0`1.<ForWorker>b__1()

Inner Exception 1:
UpdateException: An error occurred while updating the entries. See the inner exception for details.

Inner Exception 2:
SqlException: Transaction (Process ID 100) was deadlocked on lock | communication buffer resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

The SQL table looks like this in SSMS

Answer 1

As seen in the SSMS screenshot, there seem to be no indication of a primary key. There should have been a key symbol next to the ID column.

Further inspection reveals that Id is indeed declared as identity (SQL Server for AUTO INCREMENT), but not as primary key. To make Id a real primary key right click the table in SSMS and choose Design, right click the Id row in the column designer and click SET PRIMARY KEY:

After this, the stress tests runs without deadlocking itself.