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Principles of Capacity Management
When creating a system it is common knowledge that its performance is important, since users of the system will be put off it is deemed to be too slow. It is also common knowledge that performance testing tools such as OpenSTA can create load tests to help make sure that your system will perform. The use of these and other tools and techniques to make sure that the system as a whole performs well is, however, rather less well understood. This document outlines an approach to fitting performance testing into a company’s development process and so provides a context for managing system performance.
The document is intended for anyone who needs to understand how to go about verifying the likely performance of a developed system, and to make sure that an appropriate approach is used to manage the performance of the system. The document more describes the management approach required for the Capacity Planning and Management, rather than going into the technical details. As such, it does not assume detail technical knowledge or go into the mathematical basis for performance modelling or testing.
Free Performance Model
A second item that I have decided to make available is a “Generic Performance Model”. This model is built as a large Excel Spreadsheet (20Mb download). Using it allows examination of how system performance may vary with user demand, time and system calibration parameters. Since it is a large spreadsheet it takes a while to re-calculate when changes are made, but it does allow useful evaluation of the likely behaviour of a system. Some caution is needed in using it as the usual IT principle of “Garbage in, garbage out” applies. I will provide documentation of the various pages of the model over the next few month in our bulletin, or please feel free to join my web site and ask questions there.
The model may be downloaded from Generic Performance model v 1.02, and more information about using it can be obtained here:
Please Note: The spreadsheet comes for use “as is”. If I find, or am informed about, defects I will resolve them – then provide feedback in the forums of my web site and in the next monthly bulletin. It is, however, a complex spreadsheet which I am providing for free and so can not provide a guarantee beyond this.
I find it surprising how often I end up reinventing the wheel when it comes to project estimation. I suspect that there are others out there who end up doing the same, and so I decided that it was past time that I standardised my personal approach to project estimation using a model spreadsheet. Approaches and standards for estimation vary, but my preferred approach to a second cut estimate is:
- Work out the set of scenarios that apply to the project being built.
- Estimate each using a complexity rating (High, Medium, Low etc.).
- Adjust this according to how complex the project is likely to be.
- Use this to work out the likely number of man-days that the project is likely to take, based on appropriate experience and best-guesses.
- Map this to an effort estimate, and hence to a likely team size and duration.
It is this approach that I have implemented as a spreadsheet model for future, and general, use. The spreadsheet is available for download here:
More details on the model and its usage can be found here: