Monday, February 04, 2013

Line-by-line profiling with dotTrace Performance

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dotTrace Performance allows us to profile an application in several ways. We can choose between sample profiling, tracing profiling and line-by-line profiling. Generally sampling profiling is used first to acquire a high-level overview of call performance in an application, after which tracing and line-by-line profiling is used to close in on a performance issue.

Profiling types

Sampling is the fastest and the least precise mode of profiling. With sampling, dotTrace basically grabs current call stacks on all threads once in a while. When capturing a snapshot, the number of calls isn’t available and times are approximate. Accuracy cannot be more than the sampling frequency.

Tracing is slower yet more precise than sampling. Instead of grabbing call stacks on all threads, tracing subscribes to notifications from the CLR whenever a method is entered and left. The time between these two notifications is taken as the execution time of the method. Tracing gives us precise timing information and the number of calls on the method level.
Line-by-line is the slowest yet most precise mode of profiling. It collects timing information for every statement in methods and provides the most detail on methods that perform significant work. We can specify exactly which methods we want to profile or profile all methods for which dotTrace Performance can find symbol information.

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