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How to determine the maximum number of concurrent connections my server can handle.

Posted on 2003-10-31
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Last Modified: 2012-05-04
I have an application that runs through a web browser.  I have a dedicated T1 line between us and another company.  This is the ONLY transactions done on this T1.   I am trying to determine how much bandwidth my app uses from the time the user send a request to me and gets a response back to them.  Then I want to use that info to determine what would potentially be the maximum number of users that could connect to this server at one time.  

(P.S.  the server is a 2.4 Ghz, with 1 + Gig of RAM, and 80 Gig HDD.....defintely enough power).

How do I determine the bandwidth usage with my App?
How do I determine the maximum # of users?  And is there a free solution?

Please Help!
Thanks.
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Question by:harboramerican
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by:Tacobell777
ID: 9660653
Are you using IIS6 or 5
I think you are talking about 6.

If you are talking about limiting the bandwidth, then I would not even fool with it, man you got a T1...!

Unless this customer is paying you for a certain amount of bandwidth? Then I would limit it to what he is paying for.

If this is IIS6 and your talking about limiting the number of users, I would also not bother with it, or set it to a realistic amount, for example if you reckon only 10 people would connect to at a time then set it to 15 or something.

Why exactly do you want to limit anything?

Anyway, to sort of answer your question, I guess you would use http://www.paessler.com/prtg/ to see what badwidth your site uses. And you can use any other statistics software to analyse your logs, for example with www.webtrends.com/ or http://www.eiqnetworks.com/products/webanalytics.shtml and then determine your settings by looking at that.
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by:harboramerican
ID: 9660832
Where's the answer?
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Author Comment

by:harboramerican
ID: 9660843
I am not wanting to LIMIT anything.  I am wanting to be able to determine (on IIS 5) what the maximum number of concurrent connections is that I could handle, so that the customer knows what the limitations are and what they can expect.
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by:heskyttberg
ID: 9669730
Hi!

This question isn't easily answerd.
You do know http is stateless protocol, right ?

When I started my first webapp in Java I had a hard time learning this, but eventually got it.
Ok exact bandwith is hard, but calculate like this:
http add 10%
https add 33%

Follow theese steps and you'll get an idea:
1. User make a request, this bandwith can be ignored, unless it's a form.
2. In IE for example, save down everything that displays in page and check how much disk it takes up.
    Add it all up, and you get a pretty good picture on how many kb got transfered to the client.
3. Repeat 2 for all pages you want to calculate for.

So let's say one response genreates a page that is 250kb.
If HTTPS it's about: 330kb transferd.
If HTTP it's about: 275kb transferd.

I'll take the HTTP as example.
275Kb is about 2200kbit, whic is about 2.14Mbit.
T1 about 1.54Mbit is about

So one such request will take all bandwith for just over 1 second.

Now it depends on how long time is the longest you want the users to have to wait before the page is loaded.
Let's say 5 sec is maximum.
Then you can allow 5 exactly concurrent users, this rarely occurs so you can multiple this with 1.5-2.
In this case I would say no more then 10 users on the T1 or it will start go very slow for everyone.

This example you can use to calculate yourself how much is needed. The smaller the total page are in kb, the more number of users you can have.

Hope this will help you to figure out a reasonable number yourself.

Regards
/Hasse
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by:fz2hqs
ID: 9671151
With all due repect to the other contributors all the calculations could be a bit of a waste, as you may find yourself processor or memery bound first. Depending on what your application does and how well it does it you could find (in the absolute worse case scenario) that you might only be able to support a couple of concurrent conncections - very unlikley I know but is possible. Given a T1 line, and that you have IIS5 I am guesing that it is asp based ? maybe a database too ? A well written app should be able to serve on that spec machine up to 250 concurrent *sessions* That would depend on what other bits of software where running, how big the databases are and how well written the app is.

You best bet would be to run some kind of stress testing software otherwise you are looking at an equation with too many unknowns
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Accepted Solution

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heskyttberg earned 30 total points
ID: 9676862
Hi!

Well with all due respect to fz2hqs, In this case it's quite obvious that the bottleneck is bandwith, not the server itself.
It's almsot impossible to write an app so bad that such a server wouldn't be able to serve at least 100 users and since bandwith is limited to a T1 about 100 users would mean each user get about 15kbit each and that isn't very good.

So the limit is bandwith in this case.
If the server would be on 100Mbit connection, the limit would be the server, then you would have to do a load test to know for sure.

Only time the server would become a bottleneck here is if there are going to be a BIG database, then you might have to consider using SCSI drives instead of IDE.

Regards
/Hasse

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