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What do Appstats mean?

Take this data from post from the Engine Block application as an example:

real = 107ms cpu = 141ms api = 388ms overhead = 1ms RPC Total: 63ms (388ms api) Grand Total: 107ms (530ms cpu + api)

I think I understand the overhead: it gives the time taken to write the logs, with the exception of the time taken to save the logs to memcache.

I am confused by other numbers:

  • What exactly do real, cpu and api mean?
  • How does api differ from total RPC?
  • What is "Grand Total"?
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This is my understanding:

  • real is the time measured by the clock. This time has passed.

  • api uses the time spent on RPC, for example, access to the data warehouse. This is not true time, but a certain amount of computing resources, measured in time.

  • cpu uses the time taken to execute the code. Again, this is not really time, but the use of resources measured in time.

  • api differs from RPC Total only in that the total number of RPC shows the number of hours elapsed during api . Due to parallelism, it is possible to compute 388 ms in 63 Ξs. Thus, RPC Total shows both the time spent and the use of resoure.

  • Grand Total - the total time of the wall (the same as real ), with the sum of cpu , api and overhead . In this case, 530 ms of quotas are used in 107 ms.

  • overhead is, of course, time "wasted", waiting for "real" work. This mainly includes resources received by AppStats itself.

See Appstats: RPC Instrumentation for Google App Engine by Guido van Rossum for more information.

Guido van Rossum made a presentation on Google I / O 2010 called Appstats - Instrumentation for the App Engine , where he briefly discusses this. This is a great conversation to learn about the App Engine, as well as optimization and tools in general. This is about an hour.

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