Software Performance and Scalability: A Quantitative Approach

Introduction

	All good things start with smart choices.
	--Anonymous

PERFORMANCE VERSUS SCALABILITY

Before we start, I think I owe you an explanation about what the difference is between performance and scalability for a software system. In a word, performance and scalability are about the scalable performance for a software system.

You might find different explanations about performance versus scalability from other sources. In my opinion, performance and scalability for a software system differ from and correlate to each other as follows:

• Performance measures how fast and efficiently a software system can complete certain computing tasks, while scalability measures the trend of performance with increasing load. There are two major types of computing tasks that are measured using different performance metrics. For OLTP (online transaction processing) type of computing tasks consisting of interactive user activities, the metric of response time is used to measure how fast a system can respond to the requests of the interactive users, whereas for noninteractive batch jobs, the metric of throughput is used to measure the number of transactions a system can complete over a time period. Performance and scalability are inseparable from each other. It doesn't make sense to talk about scalability if a software system doesn't perform. However, a software system may perform but not scale.

• For a given environment that consists of properly sized hardware, properly configured operating system, and ...