Articles by Neil Gunther

Go Guerrill… R on Your Data in August

July 5, 2010 | Neil Gunther

Only one month to go! 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 t... [Read more...]

Prime Parallels for Load Balancing

July 5, 2010 | Neil Gunther

Having finally popped the stack on computing prime numbers with R in Part II and Part III, we are now in a position to discuss their relevance for computational scalability.My original intent was to show how poor partitioning of a workload can defeat the linear scalability expected when full ... [Read more...]

Linear Modeling in R and the Hubble Bubble

June 22, 2010 | Neil Gunther

Here is a scatter plot with the coordinate labels deliberately omitted. Figure 1. Do you see any trends? How would you model these data? It just so happens that this scatterplot is arguably the most famous scatterplot in history. One aficionado, writing more than forty years after its publication, commented skeptically [1]:"[... [Read more...]

Playing with Primes in R (Part II)

June 17, 2010 | Neil Gunther

Popping Part III off the stack—where I ended up unexpectedly discovering that the primes and primlist functions are broken in the schoolmath package on CRAN—let's see what prime numbers look like when computed correctly in R. To do this, I've had to roll my own prime number generating ... [Read more...]

Primes in R (Part III): Schoolmath is Broken!

June 13, 2010 | Neil Gunther

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 ... [Read more...]

Go Guerrill-R on Your Data in August

June 8, 2010 | Neil Gunther

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...
[Read more...]

Simulating a Queue in R

May 30, 2010 | Neil Gunther

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 simulatio...
[Read more...]

Load Testing Think Time Distributions

May 20, 2010 | Neil Gunther

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 yoursel...
[Read more...]

Emulating Internet Traffic in Load Tests

May 15, 2010 | Neil Gunther

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, ...
[Read more...]

Significant Figures in R and Rounding

April 16, 2010 | Neil Gunther

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...
[Read more...]

Significant Figures in R and Info Zeros

April 11, 2010 | Neil Gunther

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 m...
[Read more...]

Negative Scalability Coefficients in Excel

May 12, 2009 | Neil Gunther

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 (...
[Read more...]

Barry3-Apdex Also Lives in R

April 17, 2009 | Neil Gunther

As a by-product of my presentation on the Apdex Index at the NorCal CMG meeting, back in February, Guerrilla graduate, Stephen O'Connell, went off and did an implementation in R. You can read about it in this month's CMG MeasureIT and download his R-s...
[Read more...]

PDQ 5.0 is on the Launch Pad

April 4, 2009 | Neil Gunther

PDQ (Pretty Damn Quick) major release 5.0 is on the launch pad at Cape SourceForge. Because of a potential collision with the North Korean ICBM/satellite launch, we won't be filling the main liquid-hydrogen tank until next week (we don't want PDQ blame...
[Read more...]

Modern Microprocessor MIPS

April 2, 2009 | Neil Gunther

The question of how modern microprocessors compare with mainframe processors of yore, arises from time to time. The vernacular rate metric that has persisted for a long time (long in the history of computers, that is) is MIPS. Whether you approve of M...
[Read more...]

Plotting PDQ Output with R

February 27, 2009 | Neil Gunther

One the nice things about PDQ-R (coming in release 5.0) is the ability to plot PDQ output directly in R. Here's a PDQ-R script, together with the corresponding graphical output, that I knocked up to show the effect on the throughput curve of adding mor...
[Read more...]
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