Jomo Fisher--Rico Mariani has been posting about LINQ to SQL perfomance and has finally posted the performance numbers for Beta2: http://blogs.msdn.com/ricom/archive/2007/07/05/dlinq-linq-to-sql-performance-part-4.aspx
One of the tricks Rico and Matt Warren used to get this stellar performance was to generate IL at run time. I learned this design pattern from Matt and used it on a completely different problem (see http://blogs.msdn.com/jomo_fisher/archive/2007/03/28/fast-switching-with-linq.aspx) to get a 900% performance improvement. I don't know whether this pattern already has a name (Dynamic Compilation seems to fit) but it's hard to ignore its potential for significant performance improvement in a particular class of problem. A further benefit is that you can hide a lot of complex, deep thinking code behind a simple interface that you present to your user.
Correction: Now that I think about it, I may have originally learned this pattern from my high school friend Brandon D'Souza who used it to compile equations into Apple II machine language. This was for a spread sheet application our teacher wanted to call 'Rickards High Scool 1-2-3-4.'
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