Publications by Neil Gunther
Response Time Percentiles for Multi-server Applications
In a previous post, I applied my rules-of-thumb for response time (RT) percentiles (or more accurately, residence time in queueing theory parlance), viz., 80th percentile: $R_{80}$, 90th percentile: $R_{90}$ and 95th percentile: $R_{95}$ to a cellphone application and found that the performance measurements were not completely consi...
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Facebook Meets Florence Nightingale and Enrico Fermi
Highlighting Facebook’s mistakes and weaknesses is a popular sport. When you’re the 800 lb gorilla of social networking, it’s inevitable. The most recent rendition of FB bashing appeared in a serious study entitled, Epidemiological Modeling of Online Social Network Dynamics, authored by a couple of academics in the Department of...
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Melbourne’s Weather and Cross Correlations
During a lunchtime discussion among recent GCaP class attendees, the topic of weather came up and I casually mentioned that the weather in Melbourne, Australia, can be very changeable because the continent is so old that there is very little geographical relief to moderate the prevailing winds coming from the west. In general, Melbou...
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Importing an Excel Workbook into R
The usual route for importing data from spreadsheet applications like Excel or OpenOffice into R involves first exporting the data in CSV format. A newer (c. 2011) and more efficient CRAN package, called XLConnect, facilitates reading an entire Excel workbook and manipulating worksheets and cells programmatically from within R. XLCon...
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How to Remember the Poisson Distribution
The Poisson cumulative distribution function (CDF) \begin{equation} F(α,n) = \sum_{k=0}^n \dfrac{α^k}{k!} \; e^{-α} \label{eqn:pcdf} \end{equation} is the probability of at most $n$ events occurring when the average number of events is α, i.e., $\Pr(X \le n)$. Since \eqref{eqn:pcdf} is a probability function, it cannot have a val...
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Restaurant Performance Sunk by Selfies
An interesting story appeared over the weekend about a popular NYC restaurant realizing that, although the number of customers they served on a daily basis is about the same today as it was ten years ago, the overall service has significantly slowed. Naturally, this situation has led to poor online reviews so, the restaurant hired a f...
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Hockey Elbow and Other Response Time Injuries
You’ve heard of tennis elbow. Well, there’s a non-sports, performance injury that I like to call hockey elbow. An example of such an “injury” is shown in Figure 1, which appeared in a recent computer performance analysis presentation. It’s a reminder of how easy it is to become complacent when doing performance analysis and ...
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Hockey Elbow and Other Response Time Injuries
You’ve heard of tennis elbow. Well, there’s a non-sports, performance injury that I like to call hockey elbow. An example of such an “injury” is shown in Figure 1, which appeared in a recent computer performance analysis presentation. It’s a reminder of how easy it is to become complacent when doing performance analysis and ...
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PDQ Version 6.2.0 Released
PDQ (Pretty Damn Quick) is a FOSS performance analysis tool based on the paradigm of queueing models that can be programmed natively in R Python Perl C and several other languages. This minor release is now available for download. If you’re new to PDQ, here’s a simple queueing model written R that you can paste directly into an...
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PDQ Version 6.2.0 Released
PDQ (Pretty Damn Quick) is a FOSS performance analysis tool based on the paradigm of queueing models that can be programmed natively in R Python Perl C and several other languages. This minor release is now available for download. If you’re new to PDQ, here’s a simple queueing model written R that you can paste directly into an ...
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