Sunday, March 21, 2010

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.

Friday, March 19, 2010

Memcached Scalability at Velocity 2010

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

Velocity 2010 Conference

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.

Thursday, March 11, 2010

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

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.