Articles by Neil Gunther

The Social Network Ranking is Wrong

January 14, 2013 | Neil Gunther

Call me old-fashioned, but I never saw the movie The Social Network until last year (at a private screening). In case you also missed it, it's the Hollywood version of how Facebook.com came into being. Quite apart from any artistic criticisms, I have a genuine psychological problem with movies ... [Read more...]

PDQ 6.0.1 is Released

December 18, 2012 | Neil Gunther

As already described previously, the main purpose of Release 6.0.1 Build 121512 is improved compatibility and stability between PDQ and the R statistical environment. For example, many of the PDQ models, previously found in the ../examples/ directory, can now also be accessed via the demo() command in the R-console. Testing was carried ... [Read more...]

PDQ 6.0 is On Its Way

November 12, 2012 | Neil Gunther

PDQ (Pretty Damn Quick) version 6.0.β is in the QA pipeline. Although this is a major release, cosmetically, things won't look any different when it comes to writing PDQ models. All the big changes have taken place under the hood in order to make PDQ more consistent with the R statistical ... [Read more...]

PostgreSQL Scalability Analysis Deconstructed

April 11, 2012 | Neil Gunther

In 2010, I presented my universal scalability law (USL) at the SURGE conference. I came away with the impression that nobody really understood what I was talking about (quantifying scalability) or, maybe DevOps types thought it was all too hard (math). Since then, however, I've come to find out that people ... [Read more...]

How to Generate Exponential Delays

March 21, 2012 | Neil Gunther

This question arose while addressing Comments on a previous blog post about exponentially distributed delays. One of my ongoing complaints is that many, if not most, popular load-test generation tools do not provide exponential variates as part of a library of time delays or think-time distributions. Not only is this ... [Read more...]

Green Disk Sizing

February 3, 2012 | Neil Gunther

I finally got around to completing item 5 on my 2011 list concerning electrical power consumed by a magnetic hard disk drive (HDD). The semi-empirical statement is: Power ∝ Nplatters × Ω2.8 × D4.6    . . .    (1) where Nplatters is the number of platters on the spindle, Ω is the rotational speed in revolutions per minute (RPM) and D the ... [Read more...]

Visual Illusions: Google vs Facebook vs Yahoo

October 3, 2011 | Neil Gunther

The ability to visualize data, enabled by the advent of graphical computer tools, has been a great boon to Cap and Perf. The power derives from the way graphical displays provide an efficient impedance match to the visual system in our brain. The weakness derives from the way graphical displays ... [Read more...]

Subjugation to the Sigmas

August 23, 2011 | Neil Gunther

No doubt you've heard about the tyranny of the 9s in reference to computer system availability. You're probably also familiar with the phrase six sigma, either in the context of manufacturing process quality control or the improvement of business processes. As we discovered in the recent Guerrilla Data Analysis Techniques ... [Read more...]

GDAT 2011 in Review

August 13, 2011 | Neil Gunther

As usual, the Guerrilla Data Analysis Techniques (GDAT) class was a total blast. Motivated students always guarantee that. It would really help our scheduling, however, if people didn't wait until the last nanosecond to register for the class. But give... [Read more...]

Q-Q Plots for Multi-modal Performance Data

August 3, 2011 | Neil Gunther

I'm in the process of putting together some slides on how to apply Quantile-Quantile plots to performance data. Q-Q plots are a handy tool for visually inspecting how well your data matches a known probability distribution (prob dsn). If the match is g... [Read more...]

A Winking Pink Elephant

June 27, 2011 | Neil Gunther

The title of chapter 5 in my Guerrilla Capacity Planning book is, "Evaluating Scalability Parameters," and underneath it you'll see this quote:"With four parameters I can fit an elephant. With five I can make his trunk wiggle." —John von NeumannIn that vein, Guerrilla alumnus Stephen O'C. pointed me at a ... [Read more...]

Go Guerrill-R on Your Data

May 31, 2011 | Neil Gunther

The Guerrilla Data Analysis Techniques training course (GDAT) will be held during the week of August 8-12 this year. As usual, the focus will be on applying R to your performance and capacity planning data, as well as how to use the PDQ-R modeling too... [Read more...]

May 2011 Guerrilla Classes: Light Bulb Moments

May 23, 2011 | Neil Gunther

It's impossible to know what will constitute a light bulb moment for someone else. In the recent Guerrilla classes (GBoot and GCaP), we seemed to be having many more than our usual quota of such moments. So much so, that I decided to keep a list. The first was mine. ... [Read more...]

Applying PDQ in R to Load Testing

May 19, 2011 | Neil Gunther

PDQ is a library of functions that helps you to express and solve performance questions about computer systems using the abstraction of queues. The queueing paradigm is a natural choice because, whether big (a web site) or small (a laptop), all computer systems can be represented as a network or ... [Read more...]

Reporting Standard Errors for USL Coefficients

November 13, 2010 | Neil Gunther

In a recent Guerrilla CaP Group discussion, Baron S. wrote:....BS__ Using gnuplot against the dataset I gave, I get BS__    sigma   0.0207163 +/- 0.001323 (6.385%) BS__    kappa   0.000861226 +/- 5.414e-05 (6.287%) The Gnuplot output includes the errors for each of the universal scalability law (USL) coefficients. A question about the magnitude of these errors ... [Read more...]

Confidence Bands for Universal Scalability Models

September 7, 2010 | Neil Gunther

In the recent GDAT class, confidence intervals (CI) for performance data were discussed. Their generalization to confidence bands (CB) for scalability projections using the USL model also came up informally. I showed a prototype plot but it was an ugly hack. Later requests from GDAT attendees to apply CBs to ... [Read more...]

Where to Start with PDQ?

August 30, 2010 | Neil Gunther

Once you've downloaded PDQ with a view to solving your performance-related questions, the next step is getting started using it. Why not have some fun with blocks? Fun-ctional blocks, that is. Since all digital computers and network systems can be considered as a collection of functional blocks and these blocks ... [Read more...]

Excel Errors and Other Numerical Nightmares

August 25, 2010 | Neil Gunther

Although I use Excel all the time, and I strongly encourage my students to use it for performance analysis and CaP, I was forced to include a warranty disclaimer in my GCaP book because I discovered a serious numerical error while writing Appendix B. There, my intention was just to ... [Read more...]

Gone Guerrill_ R on Our Data

August 16, 2010 | Neil Gunther

Here's a summary of some things we learnt about applying R to computer performance and capacity planning data in the GDAT Class last week. Neural nets pkg nnet applied to CPU performance data in the Ripley and Venables book (see Section 8.10). How to do stacked plots that Jim calls "spark ... [Read more...]
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