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On 05/29/2012 05:42 PM, Doug Hellmann wrote:
> IIRC, the meters discussed in the wiki [1] are supposed to show "delta" values (usage since the last time an event was generated), although the "Alternate Gauge Design" section discusses cumulative meters instead. The libvirt pollsters we have now produce cumulative data, and it might be complicated and error-prone to change them to compute the deltas internally before generating events. On the other hand, some of the other counters may be more complicated to generate as cumulative values.
>
> Rather than taking an either/or approach, I propose we document for each counter whether it uses the delta or cumulative approach. The API server can ask the meter plugin for that piece of information when calculating the aggregate value so that the caller does not have to keep track of the rules for each meter.
>
I tend to prefer using a gauge and I agree that documenting what was preferred (gauge or delta) for a given meter / counter is enough.

My 2ct ;-)

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Loïc Dachary         Chief Research Officer
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