Visual Proof of Little's Law Reworked

Back in early March, when I was at the Hotsos Symposium on Oracle performance, I happened to end up sitting next to Alain C. at lunch. He always attends my presentations, especially on USL scalability analysis. During our lunchtime conversation, he took out his copy of Analyzing Computer System Performance with Perl::PDQ and opened it at the section on the visual proof for Little's law. Alain queried (query ... Oracle ... Get it?) whether the numbers really added up the way they are shown in the diagrams. It did look like there could be a discrepancy but it was too difficult to reanalyze the whole thing over lunch.

Hotsos 2013: Superlinear Scalability

As readers of this blog know, the Universal Scalability Law (USL) is a framework for quantifying performance measurements and extrapolating load-test data. Applied as a statistical regression model, the two USL contention (α) and coherency (β) parameters numerically indicate the degree of sublinear scalability in the data, i.e., how much linear scaling you're losing due to sharing and consistency overheads. Some examples of USL scalability analysis applied to databases, include:

• VoltDB
• Postgres
• My USL analysis of the Postgres data

More recently, it was brought to my attention that the USL fails when it comes to modeling superlinear performance (e.g., see this Comments section). Superlinear scalability means you get more throughput than the available capacity would be expected to support. It's even discussed on the Wikipedia (so it must be true, right?). Nice stuff, if you can get it. But it also smacks of an effect like perpetual motion.

Every so often, you see a news report about someone discovering (again) how to beat the law of conservation of energy. They will swear up and down that it works and it will be accompanied by a contraption that proves it works. Seeing is believing, after all. The hard part is not whether to believe their claim, it's debugging their contraption to find the mistake that has led them to the wrong conclusion.

Similarly with superlinearity. Some data are just plain spurious. In other cases, however, certain superlinear measurements do appear to be correct, in that they are repeatable and not easily explained away. In that case, it was assumed that the USL needed to be corrected to accommodate superlinearity by introducing a third modeling parameter. This is bad news for many reasons, but primarily because it would weaken the universality of the universal scalability law.

To my great surprise, however, I eventually discovered that the USL can accommodate superlinear data without any modification to the equation. As an unexpected benefit, the USL also warns you that you're modeling an unphysical effect: like a perpetual-motion detector. A corollary of this new analysis is the existence of a payback penalty for incurring superlinear scalability. You can think of this as a mathematical statement of the old adage: If it looks too good to be true, it probably is.

I'll demonstrate this remarkable result with examples in my Hotsos presentation.

Hotsos Symposium 2012

Time Bandits: How to Analyze Fractal Query Times

Tues, March 6, 2012 @ 2:15 pm

That's the title of my presentation at this year's Hotsos Symposium and no, I won't be trying to make any obscure connections between Terry Gilliam's famous movie and Oracle database products (as interesting as that exercise might be).

Instead, I'll be talking about fractals in time and how they can impact performance—especially Oracle database performance. The responsiveness of your Oracle application can be lost for longer than expected periods of time, ostensibly stolen by time bandits.

Preview Slides (2012). A more detailed explanation of the fractal technique used is now provided in the Guerrilla Data Analytics (GDAT) class: How to Get Beyond Monitoring from Linear Regression to Machine Learning.

Hotsos 2011: Brooks, Cooks, Delay and This Just In ...

Thanks to all those who attended my presentation and offered me their compliments afterwards. It was a bit rushed and went a bit wobbly when it came to the description of the repairman queueing model (the Apple Genius Bar), but I knew that might happen going in. Despite my best efforts to muddle it at times, it seems people were able to take away a coherent (pun!) message. That was also evident from the excellent audience questions, as well as some of the tweets I've seen. Thank you.

Hotsos 2011: Mine the GAPP

It's that time of year again so, here I am in Dallas to present "Brooks, Cooks, and Response Time Scalability," where I will be showing how my universal scalability law (USL) can be applied to quantifying response-time scaling; as opposed to the more typical throughput scaling.

Cooking Up Some Hotsos for 2011

Just got word that my proposed presentation "Brooks, Cooks and Response Time Scalability" has been accepted for the Hotsos Symposium, March 2011 in Dallas, Texas.

Hotsos is a great conference that is Oracle-related but not Oracle-sponsored. As the name implies, the focus is on the performance of Oracle databases and applications, but it's been my experience that attendees are very keen to know about performance techniques, not matter what their context.

Hotsos 2011 will give me an opportunity to expand on my Nov 2007 observation that the USL contains a representation of the mythical man-month. In other presentations I've always talked about characterizing throughput scalability, but this time I'll extend the USL to quantifying response-time scalability.

Hotsos 2008: Day 3

Only two things happened today; I gave my presentation on "Better Performance Management through Better Visualization Tools" and I met with Bob Sneed because he also asked my to review his presentation.

Hotsos 2008: Day 2

Tanel Poder continued his theme of better ways to collect Oracle performance data by demonstrating how his "Sesspack" (Oracle session level) data could be visualized using VBA calls to Excel charting functionality. He used Swingbench as a load generator for his demos. Afterwards, I spoke with him about my talk tomorrow and he said he was interested and would attend.

Hotsos 2008: Day 1

Like last year, the Hotos 2008 Oracle performance symposium continues to be a class act.

Hotsos Oracle Symposium 2008

I've been invited to speak again at the Hotsos Oracle Symposium, March 2-6 in Dallas, Texas. I'm more than happy to do this because I found last year's symposium to be a first class operation with plenty of great speakers and an attentive audience who were very interested in performance analysis and capacity planning in general, in addition to it's applicability for ORACLE.

Just as an aside, if you look at the Hotsos company logo at the top of their web pages, you'll see some equations or bits of equations. The first of these is the denominator of the famous Erlang-C function (A. Erlang, 1917). More on that in an upcoming blog entry.

Hotsos 2007 Sizzled!

Just returned from Dallas where I was an invited speaker at the Hotsos 2007 Symposium on ORACLE performance. This symposium was a class operation: great hotel, great people, great food, great presentations, etc. and, as a newbie, I was treated very well. It seems that Cary Milsap (the energy behind the symposium) had already greased the runway for me, so I found myself to be a known quantity to many of the attendees, even though I had never met them before. This was way cool (Thanks, Cary).

Although ostensibly a group of very enthusiastic ORACLE performance people (about 450 attendees), they are not bigots, so they are interested in all aspects of performance. Moreover, Oracle performance gets critiqued. Capacity planning is one aspect that is new for many of them and I was a member of a panel session on that topic. During the 24 hours I was there, I attended a very interesting session on the measured limitations of RAC 10g scalability for parallel loads (ETL) and queries against a large-scale data warehouse (DWH), and a talk on how data skew can impact the kind of performance conclusions you tend to draw. But perhaps the most interesting things that I learnt came out of several spontaneous discussions I had with various folks, including some conversations that went into the wee hours of Monday morning. My only regret was that I couldn't stay longer. I definitely plan to attend Hotsos 2008.