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Many PerformanceGuard graphs and widgets—for example the Application Chart widget—are able to show the availability of applications, servers, etc., but what is availability?


 When is something considered to be available?

To answer this we need to look at response times: If response times are so long that use of a service, website, transaction or similar becomes impossible, PerformanceGuard considers the service, etc. to be unavailable. By default, PerformanceGuard loses its patience with a service, etc. if it hasn't responded within 500,000 milliseconds (that's a little more than eight minutes). Everything that's not unavailable, is considered by PerformanceGuard to be available. So, if you see that a service has been 100% available during the last week, it means that it has not exceeded the acceptable response time limit during the last week.

 Do you measure availability of application pings (HTTP requests, ICMP ping and/or traceroutes)?

For application pings, PerformanceGuard looks not only at acceptable response times, but also at whether a response is expected or not: If the response is unexpected, for example if the response has a response code of 404 Not Found, PerformanceGuard considers the service to be unavailable, even if the response was received within acceptable time.

 How does PerformanceGuard calculate the availability %?

PerformanceGuard looks at the ratio between failed requests and all requests in percent. In other words: (all requests − failed requests) / all requests × 100

 I just set up a new server. Nobody has used it yet. How can it be 100% available?

Bear in mind that PerformanceGuard looks at your new server based on how the PerformanceGuard agents experience it: If none of the computers with PerformanceGuard agents have used the new server, there have not been any unacceptably long response times, and the server has thus not been unavailable. Everything that's not unavailable, is considered by PerformanceGuard to be available, and that explains the 100% availability, even though nobody has yet used your new server.

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