On Wed, Oct 31, 2012 at 1:39 PM, Julien Danjou <jul...@danjou.info> wrote:
> On Wed, Oct 31 2012, Eoghan Glynn wrote: > > > Would we have also have some 'misses' with the cumulative approach > > when the ceilometer agent was down? > > No, unless the counter resets several times while your agent is down. > But delta has the same issue. > > > If I understood the (\Sigma local maxima)-first idea correctly, > > the usage up to the first polling cycle would always be > > discounted from any duration. > > No, because if you have: > > Time | Value > 0 | 10 > 1 | 30 > 2 | 50 > 3 | 80 > 4 | 100 > > If your delta-pollster is down at 1 and 2, you restart at 3, therefore > at 4 you'll send "20" as usage (100 minus 80). So you miss the delta > between 10 (time 0) and 80 (time 3) (therefore 70 for free!). > If you send right away 80 at time 3 when restarting, the API will be > able to guess that between 0 and 3 the value went from 10 to 80. > With delta approach, the API cannot guess that. > Sure it can, you just need to move where the caching is done. Using a local cache to maintain the previous time a value was published you would know at time 3 that the last published value was 10, and so send 70. So the total will be correct. Doug
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