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    <p>Use a dynamic array T[] of large integers or something where T[n] counts the numer of times the response time was n milliseconds. If you really are doing statistics on a server application then possibly 250 ms response times are your absolute limit anyway. So your 1 KB holds one 32 bits integer for every ms between 0 and 250, and you have some room to spare for an overflow bin. If you want something with more bins, go with 8 bit numbers for 1000 bins, and the moment a counter would overflow (i.e. 256th request at that response time) you shift the bits in all bins down by 1. (effectively halving the value in all bins). This means you disregard all bins that capture less than 1/127th of the delays that the most visited bin catches.</p> <p>If you really, really need a set of specific bins I'd suggest using the first day of requests to come up with a reasonable fixed set of bins. Anything dynamic would be quite dangerous in a live, performance sensitive application. If you choose that path you'd better know what your doing, or one day you're going to get called out of bed to explain why your statistics tracker is suddenly eating 90% CPU and 75% memory on the production server.</p> <p>As for additional statistics: For mean and variance there are some <a href="http://people.revoledu.com/kardi/tutorial/RecursiveStatistic/index.html" rel="nofollow noreferrer">nice recursive algorithms</a> that take up very little memory. These two statistics can be usefull enough in themselves for a lot of distributions because the <a href="http://en.wikipedia.org/wiki/Central_limit_theorem" rel="nofollow noreferrer">central limit theorem</a> states that distributions that that arise from a sufficiently large number of independent variables approach the normal distribution (which is fully defined by mean and variance) you can use one of the <a href="http://en.wikipedia.org/wiki/Normality_test" rel="nofollow noreferrer">normality tests</a> on the last N (where N sufficiently large but constrained by your memory requirements) to monitor wether the assumption of normality still holds. </p>
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    1. CO<If you really are doing statistics on a server application> I am interesting in collecting more kinds of statistics, not just response times. It is not always easy to determine proper bounds. So, I'm looking for a general-purpose solution. Thanks.
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      1. USJason Kresowaty
 

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