Monday, November 19, 2007

NHibernate Access Performance Revisited

Two days ago I posted a blog titled NHibernate Access Performance. After making that post the results kept bothering me. First, the results did not seem accurate. I could not for the life of me figure out how the CodeDom optimizer performed so well when accessing private fields. I reviewed the NHibernate code over and over and could not determine how it possibly performed better than the basic getter/setter. Add to that my discovery from yesterday regarding the DateTime.Now Precision and I had to re-run these tests.

I learned that my instincts were dead on. The CodeDom optimizer for private field access isn't any faster than the basic field level access. It turns out I had a bug in my code where it was actually using the CodeDom property level access instead. I know, I know, I should be ashamed, I shouldn't write bugs! Truth be told, this was way too simple, I should have caught this earlier.

Now, due to the issue with the DateTime.Now precision issue, I decided to run my tests for 10,000,000 accesses. I figured at this point any precision issues should be insignificant. See the updated chart:

What's really interesting about these results is that the private field access now takes twice as long as the public property access when using basic reflection. This is more along the lines of what I would have expected. I do not know why 10,000,000 loops was enough to notice this difference but 100,000 loops wasn't. I wonder if there is some hit taken upon the first access of a property which is not present for a field? If I find out more about this I will write a new post.

--John Chapman


Oskar said...

You should use System.Diagnostics.Stopwatch to accurately measure the duration of some operation. This is based on the number of cpu ticks and should give sub-ms precision.

John Chapman said...

I did. See this later post:

DateTime.Now Precision Issues... Enter StopWatch!

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