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Web Performance Tuning by Patrick Killelea

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Chapter 3. Web Performance Measurement

Parameters of Performance

There are four classic parameters describing the performance of any computer system: latency, throughput, utilization, and efficiency. Tuning a system for performance can be defined as minimizing latency and maximizing the other three parameters. Though the definition is straightforward, the task of tuning itself is not, because the parameters can be traded off against one another and will vary with the time of day, the sort of content served, and many other circumstances. In addition, some performance parameters are more important to an organization’s goals than others.

Latency and Throughput

Latency is the time between making a request and beginning to see a result. Some define latency as the time between making a request and the completion of the request, but this definition does not cleanly distinguish the psychologically significant time spent waiting, not knowing whether your request has been accepted or understood. You will also see latency defined as the inverse of throughput, but this is not useful because latency would then give you the same information as throughput. Latency is measured in units of time, such as seconds.

Throughput is the number of items processed per unit time, such as bits transmitted per second, HTTP operations per day, or millions of instructions per second (MIPS). It is conventional to use the term bandwidth when referring to throughput in bits per second. Throughput is found simply ...

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