By Neil J. Gunther

To unravel functionality difficulties in glossy computing infrastructures, frequently comprising millions of servers working hundreds of thousands of purposes, spanning a number of levels, you would like instruments that transcend mere reporting. you wish instruments that permit functionality research of program workflow around the complete company. That's what PDQ (Pretty rattling quickly) presents. PDQ is an open-source functionality analyzer in accordance with the paradigm of queues. Queues are ubiquitous in each computing atmosphere as buffers, and because any software structure should be represented as a circuit of queueing delays, PDQ is a normal healthy for reading process functionality.   construction at the luck of the 1st variation, this significantly improved moment variation now contains 4 elements. half I comprises the foundational techniques, in addition to a brand new first bankruptcy that explains the relevant position of queues in profitable functionality research. half II offers the fundamentals of queueing conception in a hugely intelligible variety for the non-mathematician; little greater than high-school algebra being required. half III offers many useful examples of the way PDQ will be utilized. The PDQ handbook has been relegated to an appendix partly IV, besides recommendations to the workouts contained in every one bankruptcy. all through, the Perl code listings were newly formatted to enhance clarity. The PDQ code and updates to the PDQ guide can be found from the author's site at

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2008 Following upon the 2002 result, the author proves that his universal scalability law [Gunther 1993, 2007b] is equivalent to synchronous queueing in a machine repairman model with a linear load-dependent server [Gunther 2008]. See Sect. 12. As the preceding chronology indicates, the subject of queueing theory is younger than the theory of powered flight (Wrights 1903). After 1917, the development of queueing theory was not dormant but continued primarily within the context of manufacturing systems and formal probability theory, rather than computer and communication systems.

Essentially, it is a measure of how many things are waiting relative to how many things are being serviced. What makes the stretch factor really useful is that it can be compared easily with servicelevel targets. , quotes per hour is a common business unit of work in the insurance industry. The expected service level is called the service-level objective (SLO), and is expressed as multiples of the relevant service unit. An SLO might be documented as the average user response time is not to exceed 15 service units between the peak operating hours of 10 am and 2 pm.

At the time of this writing, the cause of the problem is not actually known, but that’s OK. Eventually it will be understood. What we do know at this point is that something is broken in the measurement process and it has to be resolved or any further load testing is simply a waste of time and resources. Notice that I am saying the data are the problem, not the model. The model, at this stage of the analysis, is nothing more than a set of ratios for which the physical meaning is very clear and unambiguous.

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