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What is PDQ?
PDQ © (Pretty Damn Quick) is open source software associated with the books Analyzing Computer System Performance with Perl::PDQ (2005) and The Practical Performance Analyst (1998, 2000). The PDQ software package may be downloaded freely from here whether or not you own a copy of the book. PDQ uses queue-theoretic paradigms to represent computer systems.
Computer system resources (whether hardware and software) are represented by queues (more formally, a queueing network-not to be confused with a data network-which could be a PDQ queueing model) and the queueing model is solved "analytically" (meaning via a combination of algorithmic and numerical procedures). Queues are invoked as functions in PDQ by making calls to the appropriate library functions (listed below 3). Once the queueing model is expressed in PDQ, it can be solved almost instantaneously by calling the PDQ_Solve() function. This in turn generates a report of all the corresponding performance metrics such as: system throughput, and system response time, as well as details about queue lengths and utilizations at each of the defined queues.
This algorithmic solution technique makes it orders of magnitude faster than setting up (and debugging; a step that is often not mentioned by simulationists) and running repeated (another step that is often glossed over) experiments to see if the solutions are statistically meaningful. PDQ solves everything as though it were in steady state. The tradeoff is that you cannot computer higher order statistics. (Actually, you can but that would be major digression here. Come to a class to find out more about that).