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Method for Estimating the Number of Concurrent Users.pdf )
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2012-07-24
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Method for Estimating the Number of Concurrent Users
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Method for Estimating the Number of Concurrent Users
Eric Man Wong
*
1. Introduction
For the sake of capacity planning and performance management, it is often necessary
to estimate the number of concurrent users of a system before it is actually put into
production. It is because the consumption of many system resources is directly related
to the number of concurrent users. Using web application as an example: the memory
usage, the CPU utilization, the number of server processes/threads, the number of
database connections and the network bandwidth utilization are all increasing
functions of the number of users concurrently logging in at the system.
Notwithstanding the importance, people often estimate the number of concurrent
users by intuition or wild guessing with little justification. In this paper, we try to
introduce a simple method to derive the number of concurrent users from some other
parameters that can be more easily estimated and justified.
2. An Unsatisfactory Method
A way people sometimes use to estimate the number of concurrent users is to assume
that it is equal to a certain percentage of the total user population. It is not a good
method because even though the user population can sometimes be reliably estimated,
the percentage figure being used is often, if not always, a magic number that has little
justification.
It should be pointed out that the percentage figure just mentioned cannot be taken as
the percentage of users who access a system in a certain period of time. In some
situations it is possible for the latter figure to be reliably estimated. For example, if we
know that every user uses a particular system once and only once in a month and there
is no preference on which day the system will be used, we can safely predict that the
percentage of users who will use the system in any one day is about 3.3% (that is, 1 /
30).
However, this figure alone cannot be used to deduce the number of concurrent users.
It is because the users who use the system on the same day do not necessarily use it at
the same time. Some users may use it in the morning, and some may use it in the
afternoon.
We are going to see in the next section a better way to do this.
*
Please email comments to emwong@asia.com
© Copyright 2004 by Eric Man Wong. All rights reserved.
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