After the first “50 ways to avoid, find and fix ASP.NET performance issues” free book, RedGate publishes a second one, even more technical, called “25 secrets for faster ASP.NET applications”. As the title hints at, the second one is less into the profiling and more into the improvement.
This is a great resource for up-to-date tips on performance, including much on the use of async / await patterns.
The book is available on http://www.red-gate.com/products/dotnet-development/ants-performance-profiler/entrypage/faster-asp-net-apps, and for more information, you can refer to Michaela Murray’s blog.
