On Wed, Oct 31 2012, Eoghan Glynn wrote: > Yep the sum of local maxima is not lossy as long as the requested > duration completely encapsulates the compute agent outage (and the > instance doesn't restart during the outage).
Actually, if there's one restart, it still _can_ be safe in certain cirumstances such as in a case like: Time | Value 0 | 1000 1 | 3000 (agent down) 2 | 0 (agent down) 3 | 80 4 | 100 If in this particular case, with the case where your agent was down at t1 and t2. The API will detect the counter reseted while the agent was down. With cumulative model, the loss is again less than the computed delta model. OTOH, both models fails to get some data with a case like: Time | Value 0 | 1000 1 | 3000 (agent down) 2 | 0 (agent down) 3 | 8000 4 | 10000 > However I was more thinking of the scenario where the duration > requested via the API is say t1..t4 in your example above. > > In any case, do we need a new measurement type, in addition to the > existing CUMULATIVE type, that captures the non-monotonic nature of > the measure and alerts the API that special handling is required to > compute say max-min? > > Something like TRANSIENT_CUMULATIVE, if that's not too much of a > mouthful. We discussed it already with Doug, and came to conclusion that we didn't, because the monotonic case is just a special case of the non monotonic one. So applying the computing method to the non-monotonic case will solve all problem. -- Julien Danjou -- Free Software hacker & freelance -- http://julien.danjou.info
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