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 management calculations. See Significant Figures in R and Info Zeros

Once we know how to identify significant digits, 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 trailing info-zeros in measured values, when it comes to rounding, signif shines. Better yet, it agrees with the Algorithm 3.2 in my GCaP book. Let's see how well it does.

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.table in R.

Plan for Guerrilla Capacity Planning in May

The next set of Guerrilla classes are coming up in May and seats are still available. Book early, book often. Update: Erm ... let me qualify that. The "Boot Camp" class is now closed, but the "Capacity Planning" class running the week of May 10 is still open.


Blast from the past. Some members of the 2006 class. Courtesy Tony Aponte
For those of you coming from international locations, here is a table of currency exchange rates.

(Click on the image for more details)
All Guerrilla classes have a certification level 1, 2, 3, but there are no prerequisites at this time.

Bandwidth vs. Latency — The World is Curved

Despite what you may have read in the press lately, neither our world nor the world of performance is flat. This is especially true of the performance metrics commonly known as bandwidth (or throughput) and latency. The performance relationship between these two metrics is curved or nonlinear. In general, this nonlinearity is a consequence of these two metrics being inversely related to each another: increase system throughput to decrease the latency of each request, and vice versa. A common misconception persists, however, that bandwidth and latency are independent performance metrics. I'm going to call that view the Flat-Earth view. Where does that view come from?

Window on the World

In part, it depends on your window to the world. When we look out a window, the Earth looks flat.

Occasionally, we are reminded that the Earth is actually curved. That's something most of us accept and expect, even if we're not aware of it all of the time.

Memcached Scalability at Velocity 2010

Totally stoked about being selected for the Web Performance track at Velocity 2010.


Here's our abstract:

Hidden Scalability Gotchas in Memcached and Friends

Neil Gunther (Performance Dynamics), Shanti Subramanyam (Oracle Corporation), Stefan Parvu (Sun Microsystems)

Most web deployments have standardized on horizontal scaleout in every tier—web, application, caching and database—using cheap, off-the-shelf, white boxes. In this approach, there are no real expectations for vertical scalability of server apps like memcached or the full LAMP stack. But with the potential for highly concurrent scalability offered by newer multicore processors, it is no longer cost-effective to ignore their underutilization due to poor, thread-level, scalability of the web stack. In this session we show you how to quantify scalability with the Universal Scalability Law (USL) by demonstrating its application to actual performance data collected from a memcached benchmark. As a side effect of our technique, you will see how the USL also identifies the most signficant performance tuning opportunities to improve web app scalability.

Human Metro Map and Performance Management

In my Guerrilla classes, I like to compare making a computer performance model (e.g., in PDQ) with model train construction. In the latter case, the goal is to make a scaled replica that includes as much realistism as possible (Aside: I'm assuming this is true, since I have no interest in making model trains). The goal for a performance model is the exact opposite, viz., to throw away as much detail as possible, while still maintaining the essential performance characteristics of the real computer system.

This notion leads to Guerrilla Mantra 2.4:

A performance model is more like a map of a metro rail system than a scaled replica of the metro railway.

Quantum Camera Cited in HP Labs Annual Report

The joint work we published last year on quantum information processing, in New Journal of Physics and Optics Express, has been cited on p. 29 of the 2009 HP Labs Annual Report.