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Forcasting Server Load and Capacity

Posted on 2005-04-07
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Last Modified: 2010-03-04
I'm trying to forecast traffic for a website that is going to be opened up to the public for free. I expect a GeeWiz factor to really push the hardware for the first month, and I'm worried about stability.

Part 1. Is there a way to forecast concurrent users without doing a market study? Could I look at an existing similar web site and use it as a base (via alexa's stats)?

Part 2. I also need to know how many concurrent users apache (on unix) can handle. Horse power (read up to 50k per server) is not a problem.

Currently, I get 100k hits per day that are internal to this international org. And I know hits do not equal actual page views or visitors. I also know (I think) that a web browser(IE) opens multiple connections (2-8) per session because users are very sticky, and that session our timeout is set at 20 minutes.


Bonus points for calculation examples for forecasting.

Thanks.

SJ.


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Question by:StevenJames
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by:Promethyl
ID: 13744827
I run something like 10.9 million page views last month... don't sweat that.

Perhaps the easiest way to find out where you server is would be to do uptime calculations 24 times a day.

Once a hour, once every four hours, whichever, for a week, run uptime.

root@trisha [/home/tomwats/www/northid/php]# uptime
 15:34:49  up 88 days, 21:58,  3 users,  load average: 3.69, 2.42, 1.45

Then, take an average of the last calculation. That's your sustained rate...

So, take all your values, and average them out. Divide by the average number of users on the box at any given moment.

Now you know how much load the average user takes up.

Now figure out how many users you might expect.

Multiply by the load for each user...

...

This doesn't address what you're going to need to do to keep the box up and running.


If you run PHP, I would reccommend eAccelerator. It's free and does memory based cache.

Consider rewriting your database intensive queries to cache for 30 seconds to 1 hour. That may save you hundreds of thousands of SQL queries...

Is this kind of what you're asking?

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Expert Comment

by:Promethyl
ID: 13744829
PS: This is a linear and not an exponetial model.
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by:StevenJames
ID: 13750151
10 million!  Cool.

What hardware & OS?
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Promethyl earned 1200 total points
ID: 13750162
I don't know if you liked my answer on the stats, so please speak to that. That's how I'd do the math.

Stats:

http://extremetracking.com/open;reloads?login=promethy

Quad Processor RHE.

Processor Information

Processor #1 Vendor: GenuineIntel
Processor #1 Name: Intel(R) Xeon(TM) CPU 2.40GHz
Processor #1 speed: 2392.090 MHz
Processor #1 cache size: 512 KB

Processor #2 Vendor: GenuineIntel
Processor #2 Name: Intel(R) Xeon(TM) CPU 2.40GHz
Processor #2 speed: 2392.090 MHz
Processor #2 cache size: 512 KB

Processor #3 Vendor: GenuineIntel
Processor #3 Name: Intel(R) Xeon(TM) CPU 2.40GHz
Processor #3 speed: 2392.090 MHz
Processor #3 cache size: 512 KB

Processor #4 Vendor: GenuineIntel
Processor #4 Name: Intel(R) Xeon(TM) CPU 2.40GHz
Processor #4 speed: 2392.090 MHz
Processor #4 cache size: 512 KB

Memory Information

Memory: 2056824k/2097024k available (1683k kernel code, 35592k reserved, 1318k data, 224k init, 1179520k highmem)

System Information

Linux trisha.promethylhosting.com 2.4.21-4.0.1.ELsmp #1 SMP Thu Oct 23 01:27:36 EDT 2003 i686 i686 i386 GNU/Linux

All this, and the machine is remarkably calm.

root@trisha [/home/proorg/www/tmp/tmp]# uptime
 22:07:49  up 90 days,  4:31,  2 users,  load average: 0.79, 1.82, 1.42
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Expert Comment

by:Promethyl
ID: 13951745
Effort was put into the answer, but the question was abondoned. Perhaps 50-100pts to the experts for the effort, and close the question as abondoned.
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