1. ## Is it Possible to Calculate Peak Load?

I am trying to help a new start-up customer come up with some possible peak performance metrics. I know how many users are expected in the first year and at what times those users will login and perform functions. I know what those functions are and have created a workload distribution of all the expected activities. From this, I believe I have an average number of performance requirements. With no previous metrics, is it possible to apply a calculation to determine what peak load would be? Any help is appreciated.

Thanks!

2. ## Re: Is it Possible to Calculate Peak Load?

I don't want to appear tongue-in-cheek with this answer, but it might come across that way.

Perhaps a book on statistical methods would help?

3. ## Re: Is it Possible to Calculate Peak Load?

I think it is a little tough to say without more information.

A statistical methods book would help but hey, this is the real world. Who has time to read one of those? [img]images/icons/smile.gif[/img]

I would check out some of these links...
http://www.performancetester.com/com...id,4/catid,97/

4. ## Re: Is it Possible to Calculate Peak Load?

AnneNova,

Your question is incomplete. Are you asking how a forecast can be made as to the number of users or prospective users try to log in, or are you doing research on how many users a configuration might be able to support? Two totally different types of information.

The maximum number of prospective users is often a system generation parameter for the number of threads that must be supported. Anyone in excess of that will simply not be able to login, so that leaves you guessing as to the number of people trying to get into your site. As your prospects count goes up, performance deteriorates, which is another deterrent. How does your system degrade? Does performance go down across the range or are there heuristics that penalize idle users or what not? How does your system handle an overload, by crashing or by graceful degradation?

There are many potential answers to your question that may or may not be answered mathematically. A possible approach is to correlate concurrent user threads with performance statistics and then to do some interpolations to determine when you may expect performance degradation that discourages people from using the site, which may be fewer than what the site technically supports.

5. ## Re: Is it Possible to Calculate Peak Load?

Thanks for the responses -

6. ## Re: Is it Possible to Calculate Peak Load?

skadamo - that link looks like it could provide some information that will help - thanks much.

7. ## Re: Is it Possible to Calculate Peak Load?

Oh come on folks, what happened to the helpful and respectful nature of the forum while I was off moving, weathering a divorce, coaching t-ball for my son and starting a business?? Read a statistical analysis book?? We both know that statistical methods are helpful here, but not until a reasonable group of assumptions are formed.

1) What is the basic daily usage pattern? For example, is this a site that is used primarily in a single time zone during business hours or something with a more even hourly distribution like, maybe google?

2) Are their predictable peaks and troughs over time? For instance does everyone log in on the 15th to pay their bill? Or is there a rush between thanksgiving and christmas to buy gifts? Or maybe a increases due to marketing campaigns?

3) Are there other situations that would cause peaks and/or troughs in user load?

4) Are there any batch or scheduled processes? Where do these fit with the items from above?

5) What is a typical user session duration? What is the session timeout value? What is the expected ratio of logout vs. timeout?

6) Since the total number of potential users is known, what is the likelihood that 100% of them will ever access the application within, say, the same hour? 50%? 25%? 10%?

With this information, building a graph - or a variety of graphs based on different values for these assumptions is a fairly simple process. None of them will likely be correct, but since we are starting with guesses and assumptions, it will give you a working range to go to the client with. From that you can pick a number that makes sense to all parties, add a safety factor and make that your test figure.

How's that??

8. ## Re: Is it Possible to Calculate Peak Load?

Thanks Scott - that helps! I have some assumptions that answer all of those questions so I should be able to build a graph.

9. ## Re: Is it Possible to Calculate Peak Load?

wb Scott...was wondering what happened to you...

10. ## Re: Is it Possible to Calculate Peak Load?

Thanks Nate, it's a LONG story as I hinted at in the post, but the bottom line is that I've got my personal life back in order and with PerfTestPlus officially off the ground, I'm back to consulting from the land of "very cool technology, but very narrow focus" employment.

I'll catch up with you more outside the forum!

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