Software Twist – Adrian Tosca Blog

Why Performance is Bad for your Software System

Posted in Software Architecture by Adrian Tosca on 2010, January 16

Performance is one of the so called non-functional requirements (or quality attributes) of a system and you can find it in most analysis documents. The fact that the analyst has written it in the analysis document is a good thing, but is it correctly specified most of the time?

When talking about performance there are many terms that are used, not every time in a consistent way. For example  one can talk about performance and mean ‘response time’ while other can understand ‘throughput’. Let’s see a list of terms that are associated with performance and their most common meaning (1):

  • Response time is the amount of time it takes for the system to completely process a request
  • Responsiveness is about how quickly the system acknowledges a request without actually processing it
  • Latency is the minimum amount of time to get a response even if there is no processing
  • Throughput is  how much processing can be done in a fixed amount of time

There are even more terms related to performance like load, load sensitivity and efficiency but these are what people generally understand when talking about performance. It is important to distinguish between these terms when talking about performance because they can have very different impact on the system. For example to improve the responsiveness of the system you most likely need to change the architecture maybe by implementing something like asynchronous processing.

But the system architecture should take into consideration a lot more than just performance. These are the most common quality attributes that need planned for a software system (2):

  • Agility is the ability of a system to be both flexible and undergo change rapidly
  • Flexibility is the ease with which a system or component can be modified for use in applications or environments other than those for which it was specifically designed
  • Interoperability is the ability of two or more systems or components to exchange information and to use the information that has been exchanged
  • Maintainability is the ease with which a software system or component can be modified
  • Reliability is the ability of the system to keep operating over time
  • Reusability is the degree to which a software module or other work product can be used in more than one computing program or software system
  • Supportability is the ease with which a software system can be operationally maintained
  • Security is a measure of the system’s ability to resist unauthorized attempts at usage and denial of service
  • Scalability is the ability to maintain or improve performance while system demand increases
  • Testability is the degree to which a system or component facilitates testing
  • Usability is the measure of a user’s ability to utilize a system effectively

Usually, modifying one of this attributes affects other attributes as well. For example improving agility will most of the time also improve maintainability. But how about performance? How does the performance improvement, such as modifying the system response time, will affect the other attributes?

Let’s take some examples of things that someone can do to improve performance and what are the effects:

  • A change from a web service interface to remote method invocation to improve the latency will negatively affect reusability
  • A change from an object oriented processing to a stored procedure to improve the response time will negatively affect flexibility and maintainability
  • A change from a clean implementation of an algorithm to an optimized one will negatively affect maintainability and testability

The following diagram illustrates the likely effects of improving the performance of a system to other attributes:

Performance vs Other Quality Attributes

Performance vs Other Quality Attributes

The performance improvement affects negatively every one of the quality attributes described above. So, it is better to carefully analyse the trade-offs of the performance improvement over the other quality attributes. Most of the time ‘enough’ performance is just the right thing to do when thinking in perspective.

1. Patterns of Enterprise Application Architecture by Martin Fowler
2. Implementing System Quality Attributes
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