Performance Analysis vs. Capacity Planning

This question came up in a (members only) Linkedin discussion group:

Often found a misconception about these terms. I'm sure this must be written in a book, but for informal discussions is always preferable to cite sources from standardization institutes or IT industry referents.

Thanks in advance

Gian Piero

Here's how I answered it.

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Throughput-Delay Curves

A colleague of mine at Yahoo.com asked me if I'd ever seen curves like this:

Not only is the answer, yes (it's a throughput-delay plot or XR plot in my notation), but that particular plot comes from my GCaP course notes. There, I use it to analyze the comparative performance of a functional multiprocessor (NS6000) and a symmetric multiprocessor (SC2000). Note how the two curves cross at around 1500 OPS. You can ask yourself why and if you can't come up with an explanation, you should be registering for a Guerrilla class. :)

The above XR plot also serves as a useful reminder that the throughput and response-time metrics are not only dependent on one another, but they are generally dependent in a nonlinear way—despite what some experts may claim:

Fundamental Performance Metrics

Baron Schwartz invited me to comment on his latest blog post entitled "The four fundamental performance metrics," which I did. Coincidentally, I happened to address this same topic in my presentation at CMG Atlanta last week. As the following slides shows, I claim there are really only 3 fundamental performance metrics (actually 2, if you want to get truly fundamental about it).

Calculating the Cost of Elastic Capacity

Neal Richter sent me the following tweet
Unfortunately, the paper ("Optimal staffing policy for queuing systems with cyclic demands," Int. J. Services and Operations Management, 2010) cited in the PhyOrg news item, that Neal tweeted, is not accessible to either him or me. Nonetheless, I found an earlier paper (2007) by the same author (Pen-Yuan Liao), which has a lot of the same words so, I'm assuming they both describe the same thing, more or less. Either way, I'm quite certain the math is the same.

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.

Bandwidth and Latency are Related Like Overclocked Chocolates

Prior to the appearance of special relativity theory (SRT) in 1905, physicists were under the impression that space and time are completely independent aspects of reality described by Newton's equations of motion. Einstein's great insight, that led to SRT, was that space and time are intimately related through the properties of light.

Space and time are related

Instead of objects simply being located at some arbitrary position x at some arbitrary time t, everything moves on a world-line given by the space-time pair (x, ct), where c is the universal speed of light. Notice that x has the engineering dimensions of length and so does the new variable ct: a speed multiplied by time. In Einstein's picture, everything is a length; there is no separate time metric. Time is now part of what has become known as space-time—because nobody came up with a better word.