Publications by Neil Gunther
Negative Scalability Coefficients in Excel
Recently, several performance engineers, who have been applying my universal scalability law (USL) to their throughput measurements, reported a problem whereby their Excel spreadsheet calculations produced a negative value for the coherency parameter (β < 0) on what otherwise appears to be an application that scales extremely well. Y...
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August Guerrilla Class: Using R for Performance Analysis
Registrations are still open for the Guerrilla Data Analysis Techniques (GDAT) class being held August 10-14, 2009. The focus will be on using R and the new release of PDQ-R for performance analysis and capacity planning.All Guerrilla classes are held at our Larkspur Landing location in Pleasanton, California; a 45-minute BART ride ...
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PDQ 5.0 Test Suite or … How I Spent My Weekend
I was planning to blog about the amazing time I had at Velocity 2009 last week, when this landed in my mailbox (edited for space and privacy): Subject: Seeking help with PDQ-R ...Date: Thu, 25 Jun 2009 15:51:21 -0500My name is James and I've been trying to learn to properly use PDQ after reading two of your books, "Guerrilla C...
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Significant Figures in R and Info Zeros
The other day, I stumbled upon the signif function in R, so I thought I’d take a look at what it does and compare it with some results discussed in Chap. 3 “Damaging Digits in Capacity Calculations” of my GCaP book, viz., Example 3.5 on page 31. The measured numbers in that example are reproduced here in Table 1 using read.tabl...
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Significant Figures in R and Rounding
This is a follow-on to my previous post about determining significant digits, or sigdigs, in performance and capacity planning calculations. Once we know how to do that, inevitably we will be faced with rounding the result of a calculation to the least number of sigdigs. Whereas the signif() function in R suffered from truncating trai...
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Emulating Internet Traffic in Load Tests
One of the recurring questions in the GCaP class last week was: How can we make web-application load tests more representative of real Internet traffic? The sticking point is that conventional load-test simulators like LoadRunner, JMeter, and httperf, represent the load in terms of a finite number of virtual user (or vuser) scripts, w...
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Load Testing Think Time Distributions
One of my gripes about some commercial load testing tools is that they only provide a think time distribution (Z) that is equivalent to uniform variates in the client-script. If you want some other distribution, you have to code it and debug it yourself. Load test generators are essentially very expensive workload simulators; especial...
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Simulating a Queue in R
In the GCaP class earlier this month, we talked about the meaning of the load average (in Unix and Linux) and simulating a grocery store checkout lane, but I didn’t actually do it. So, I decided to take a shot at constructing a discrete-event simulation (as opposed to Monte Carlo simulation) of a simple M/M/1 queue in R. We can make...
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Go Guerrill-R on Your Data in August
Guerrill-R, get it? Register now for the Guerrilla Data Analysis Techniques (GDAT) class to be held during the week of August 9-13, 2010. The focus will be on using R and the PDQ-R for computer performance analysis and capacity planning.(Click on the image for details)For those of you coming from international locations, here is a t...
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Primes in R (Part III): Schoolmath is Broken!
Here we are in Part III. Wait!? What happened to Parts I and II? Well, I started to write an article about Amdahl’s law, parallelism and prime numbers, but found myself buried three levels deep trying to resolve problems with prime numbers in R. My normal inclination is to use Mathematica for such things, but I happened to already b...
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