By Neil J. Gunther

To resolve functionality difficulties in smooth computing infrastructures, frequently comprising millions of servers operating 1000's of purposes, spanning a number of levels, you would like instruments that transcend mere reporting. you would like instruments that allow functionality research of software workflow around the whole firm. that is what PDQ (Pretty rattling quickly) offers. PDQ is an open-source functionality analyzer according to the paradigm of queues. Queues are ubiquitous in each computing surroundings as buffers, and because any software structure will be represented as a circuit of queueing delays, PDQ is a usual healthy for interpreting process performance.


Building at the luck of the 1st version, this significantly multiplied moment variation now contains 4 elements. half I includes the foundational thoughts, in addition to a brand new first bankruptcy that explains the principal position of queues in profitable functionality research. half II presents the fundamentals of queueing conception in a hugely intelligible sort for the non-mathematician; little greater than high-school algebra being required. half III offers many sensible examples of ways PDQ should be utilized. The PDQ guide has been relegated to an appendix partly IV, in addition to suggestions to the routines contained in each one chapter.

Throughout, the Perl code listings were newly formatted to enhance clarity. The PDQ code and updates to the PDQ handbook can be found from the author's website at

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Further decomposition of the timing chain in Fig. 5 Suppose the bottleneck is now found to be present somewhere in the network. It would useful if the network services link in the timing chain of Fig. 5 could be further decomposed with finer resolution to determine more precisely which network service was responsible for the bottleneck. Such a decomposed timing chain is shown in Fig. 6. In this case, there are probes corresponding to seven links instead of just three. Once again, there cannot be any missing links.

Several variants of the unix operating systems already store certain time intervals as 64-bit integers, and this trend will continue as 64-bit architectures become more ubiquitous. Currently, Perl5 does not handle 64-bit integers. 1 In the Beginning In Sects. 1 we defined the term epoch. Different computing platforms and different timing functions keep time encoded in terms of different starting epochs. 2 summarizes some of those functions available in the Perl 5 environment. These timing functions match many of those in the C library.

This approach introduces the possibility of an erroneous simulation occurring. In that case, previous computations are erased by rolling back the computation to a known error-free state. The simulation then proceeds forward using 14 1 Time—The Zeroth Performance Metric the error-free data until the next error is detected. Virtual time in the Time Warp protocol is simply the counterpart of the physical time presented by the environment. Distributed simulations lie outside the scope of this book.

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