Entity Framework SaveChanges() first call is very slow - performance

Question

I appreciate that this issue has been raised a couple of times before, but I can't find a definitive answer (maybe there isn't one!).
Anyway the title tells it all really. Create a new context, add a new entity, SaveChanges() takes 20 seconds. Add second entity in same context, SaveChanges() instant.
Any thoughts on this? :-)
============ UPDATE =============
I've created a very simple app running against my existing model to show the issue...
public void Go()
{
ModelContainer context = new ModelContainer(DbHelper.GenerateConnectionString());
for (int i = 1; i <= 5; i++)
{
DateTime start = DateTime.Now;
Order order = context.Orders.Single(c => c.Reference == "AA05056");
DateTime end = DateTime.Now;
double millisecs = (end - start).TotalMilliseconds;
Console.WriteLine("Query " + i + " = " + millisecs + "ms (" + millisecs / 1000 + "s)");
start = DateTime.Now;
order.Note = start.ToLongTimeString();
context.SaveChanges();
end = DateTime.Now;
millisecs = (end - start).TotalMilliseconds;
Console.WriteLine("SaveChanges " + i + " = " + millisecs + "ms (" + millisecs / 1000 + "s)");
Thread.Sleep(1000);
}
Console.ReadKey();
}
Please do not comment on my code - unless it is an invalid test ;)
The results are:
Query 1 = 3999.2288ms (3.9992288s)
SaveChanges 1 = 3391.194ms (3.391194s)
Query 2 = 18.001ms (0.018001s)
SaveChanges 2 = 4.0002ms (0.0040002s)
Query 3 = 14.0008ms (0.0140008s)
SaveChanges 3 = 3.0002ms (0.0030002s)
Query 4 = 13.0008ms (0.0130008s)
SaveChanges 4 = 3.0002ms (0.0030002s)
Query 5 = 10.0005ms (0.0100005s)
SaveChanges 5 = 3.0002ms (0.0030002s)
The first query takes time which I assume is the view generation? Or db connection?
The first save takes nearly 4 seconds which for the more complex save in my app takes over 20 seconds which is not acceptable.
Not sure where to go with this now :-(
UPDATE...
SQL Profiler shows first query and update are fast and are not different for first. So I know delay is Entity Framework as suspected.

Answer 1

It might not be the SaveChanges call - the first time you make any call to the database in EF, it has to do some initial code generation from the metadata. You can pre-generate this though at compile-time: http://msdn.microsoft.com/en-us/library/bb896240.aspx
I would be surprised if that's the only problem, but it might help.
Also have a look here: http://msdn.microsoft.com/en-us/library/cc853327.aspx

Answer 2

I would run the following code on app start up and see how long it takes and if after that the first SaveChanges is fast.
public static void UpdateDatabase()
{
//Note: Using SetInitializer is reconnended by Ladislav Mrnka with reputation 275k
//http://stackoverflow.com/questions/9281423/entity-framework-4-3-run-migrations-at-application-start
Database.SetInitializer<DAL.MyDbContext>(
new MigrateDatabaseToLatestVersion<DAL.MyDbContext,
Migrations.MyDbContext.Configuration>());
using (var db = new DAL.MyDbContext()) {
db.Database.Initialize(false);//Execute the migrations now, not at the first access
}
}