It includes DNS lookup time to set up the TCP connection and send the HTTP

It includes dns lookup time to set up the tcp

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control. It includes DNS lookup, time to set up the TCP connection and send the HTTP request to the server, and Internet-induced latency in receiving a response containing enough content that the browser can start to draw something (so-called “time to glass,” a term that will soon seem as quaint as “counterclockwise”). Especially when using curated PaaS, SaaS developer/operators have the most control over the code paths in their own apps: routing and dispatch, controller actions, model methods, and database access. We will therefore focus on measuring and improving responsiveness in those components. Google believes that this fact puts them under even more pressure to be responsive, so that getting a response from any Google service is no slower than contacting the service to begin with. For small sites, a perfectly reasonable way to mitigate latency is to overprovision (provide excess resources relative to steady-state) at one or more tiers, as Section 2.4 suggested for the presentation and logic tiers. A few years ago, overprovisioning meant purchasing additional hardware that might sit idle, but pay-as-you-go cloud computing lets you “rent” the extra servers for pennies per hour only when needed. Indeed, companies like RightScale offer just this service on top of Amazon EC2. As we will see, a key insight that helps us is that the same problems that push us out of the “PaaS- friendly” tier are the ones that will hinder scalability of our post-PaaS solutions , so understanding what
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kinds of problems they are and how to solve them will serve you well in either situation. What are the thresholds for user satisfaction on responsiveness? A classic 1968 study from the human- computer interaction literature ( Miller 1968 ) found three interesting thresholds: if a computer system responds to a user action within 100 ms, it’s perceived as instantaneous; within 1 second, the user will still perceive a cause-and-effect connection between their action and the response, but will perceive the system as sluggish; and after about 8 seconds, the user’s attention drifts away from the task while waiting for a response. Surprisingly, more than thirty years later, a scholarly study in 2000 ( Bhatti et al. 2000 ) and another by independent firm Zona Research in 2001 affirmed the “eight second rule.” While many believe that a faster Internet and faster computers have raised users’ expectations, the eight- second rule is still used as a general guideline. New Relic, whose monitoring service we introduce later, reported in March 2012 that the average page load for all pages they monitor worldwide is 5.3 seconds and the average Apdex score is 0.86. Summary Responsiveness measures how “snappy” an interactive app feels to users. Given today’s high-speed Internet connections and fast computers, responsiveness is dominated by latency. Service Level Objectives (SLOs) quantify responsiveness goals with statements such as “99% of requests within any 5-minute window should have a latency below 100 ms.” The Apdex score is a simple SLO measure between 0.0 and 1.0 in which a site gets “full credit” for
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  • Spring '19
  • Dr.Marcos

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