The gambler's fallacy killed by pure maths

Statistics (and the ability to gather/present) are an essential tool for performance testing. At the time of learning basic stats in high school and university I was plagued with the problem of not seeing the real life application of these tools. Sure, exercises and scenarios conducted simulated real life, but in reality, the meaning of stats escaped me. Fast forward 10 years and I am now rediscovering the joy of such measurements. In fact, those university text books get more of a workout now than previously during study.

I have already posted a few times about presenting stats using common tools like Microsoft Excel. I am still learning the stats package ‘r’ as I see that to be more powerful and extensible. In the interim I use a combination of Excel, MySQL and PHP to prepare and analyse stats. As this contract winds down and I prepare for the next, I’ve come across a useful application of stats to keep me entertained.

A friend of mine recently stumbled across a well known roulette strategy called the martingale strategy.

Originally, martingale referred to a class of betting strategies popular in 18th century France. The simplest of these strategies was designed for a game in which the gambler wins his stake if a coin comes up heads and loses it if the coin comes up tails. The strategy had the gambler double his bet after every loss , so that the first win would recover all previous losses plus win a profit equal to the original stake. Since a gambler with infinite wealth will with probability of 1 eventually flip heads, the martingale betting strategy was seen as a sure thing by those who practiced it…

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RWI 00239 The server has reached the maximum number of simultaneous connections

Once again on the topic of performance testing Business Objects, when executing a benchmark for a web intelligence report with goal being to see how many concurrent users it could support, the following error mesage was being generated in the vuser log:
RWI 00239 The server has reached the maximum number of simultaneous connections
Connection failed. The server has reached the maximum number of simultaneous connections. (Error: RWI 00239) (Error: INF )

What to do?

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Curve dampening for a custom load harness

Recently I wrote a test harness that had a ‘discovery’ mode. That is, given a target service level agreement (SLA), what transaction pacing or throughput did the load harness have to apply in order to achieve the SLA response times. Now my maths is a tad scratchy, but I knew that I could somehow figure out the equation to determine how much the load balancer should adjust throughput in order to achieve the desired response time. In my mind I pictured a horizontal line that is the target, and a sinusoidal line that is the actual response time that varies according to load. If I could just figure out how to dampen that curve, I would have the magic formula!

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