LINQ2SQL performance vs. custom DAL vs. NHibernate

Question

Given a straightforward user-driven, high traffic web application (no fancy reporting/BI):

If my utmost goal is performance (not ease of maintainability, ease of queryability, etc) I would surmise that in most cases, a roll-yourown DAL would be the best choice.

However, if i were to choose Linq2SQL or NHibernate, roughly what kind of performance hit would we be talking about? 10%? 20%? 200%? Of the two, which would be faster?

Does anyone have any real world numbers that could shed some light on this? (and yes, I know Stackoverflow runs on Linq2SQL..)

Answer 1

If you know your stuff (esp. in SQL and ADO.NET), then yes - most likely, you'll be able to create a highly tweaked, highly optimized custom DAL for your particular interest and be faster overall than a general-purpose ORM like Linq-to-SQL or NHibernate.

As to how much - that's really really hard to say without knowing your concrete table structure, data and usage patterns. I remember Rico Mariani did some Linq-to-SQL vs. raw SQL comparisons, and his end result was that Linq-to-SQL achieve over 90% of the performance of a highly skilled SQL programmer.

See: http://blogs.msdn.com/ricom/archive/2007/07/05/dlinq-linq-to-sql-performance-part-4.aspx

Not too shabby in my book, especially if you factor in the productivity gains you get - but that's the big trade-off always: productivity vs. raw performance.

Here's another blog post on Entity Framework and Linq-to-SQL compared to DataReader and DataTable performance.

I don't have any such numbers for NHibernate, unfortunately.

Answer 2

In two high traffic web apps refactoring a ORM call to use a stored procedure from ado.net only got us about 1-2% change in CPU and time.

Going from an ORM to a custom DAL is an exercise in micro optimization.