Graphic web design - CHAPTER 9 PERFORMANCE AND SCALABILITY TESTING These
CHAPTER 9 PERFORMANCE AND SCALABILITY TESTING These manifestations result in a decline in request throughput, which means that requests are left pending and response time increases. If the load continues to increase when the system is in this state, then the response time performance degrades exponentially. The point at which performance time degrades is referred to as the saturation point, or, more colorfully, the buckle zone. Capacity Assessment Usage Mappings The capacity assessment attempts to map the behavior of your environment to the graph shown in Figure 9-2. Therefore, at the end of the capacity assessment, you should be able to construct a graph similar to Figure 9-3. Figure 9-3. In this test, we successfully satisfied our expected users, and we have a buffer before we start exceeding SLAs. Figure 9-3 illustrates that the application is successfully satisfying its 500 expected users, but at 550 users the application starts exceeding its SLAs, showing that we have a 10 percent user buffer that can be supported. The buffer percentage represents your comfort zone for your application if your load never moves outside of your buffer, even during peaks, then you can sleep well at night. You should strive to maintain approximately a 25 percent buffer to allow for marketing promotions or any other significant increase in traffic. A buffer greater than 40 percent is typically too large, because it means that you are maintaining additional hardware and software licenses that really are not needed. Note Although a 25 40 percent buffer is generally ideal, you need to analyze your usage patterns to determine what is best for your environment. If your usage patterns are very volatile, then you might want a larger buffer, but if you are running an intranet application with a fixed maximum load, a smaller buffer may be sufficient.
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