Percentile
A percentile is a ratio. There are a hundred percentiles in a sample. The 95th percentile is the value that 95 percent of the sample lies below. The 99th percentile is the value that 99 percent of the sample lies below. So in terms of response times, the 95th percentile is a time period, by which 95 percent of requestors have all received a response.
What is an acceptable value for a response time is generally set by de facto industry standards.
Figure 1-6 Example of requests queuing on a Web site
Response time is measured from the time a request is made until the HTML response is received.
Web site response time is a function of:
| Raw processing time |
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| Wait time at any number of queues (see Figure | -6) |
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| Transfer time between multiple components |
Response time is a critical measurement and poor response times result in dissatisfied customers. Many Web sites fail simply because of response time issues.
A performance practitioner considers response time:
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| Under peak loading |
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| Under extreme loading (seasons such as Christmas, Easter, Thanksgiving, and so forth) |
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| Over modest dial-up connections |