Il 08/09/2014 16:49, Benoît Canet ha scritto:
>> > - create two windows, with twice the suggested expiration period, and
>> > return min/avg/max from the oldest window. Example
>> >
>> > t=0 |t=1 |t=2 |t=3 |t=4
>> > wnd0: [0,1) |wnd0: [1,3) | |wnd0: [3,5) |
>> > wnd1: [0,2) | |wnd1: [2,4) | |
>> >
>> > Values are returned from:
>> >
>> > wnd0---------|wnd1---------|wnd0---------|wnd1---------|
>
> This is neat.
Alternatively, you can make it probabilistically correct:
t=0 |t=0.66 |t=1.33 |t=2
|t=2.66
|wnd0: [0.66,2) | |wnd0: [2,3.33) |
wnd1: [0,0.66) | |wnd1: [1.33,2.66) | |
Return from:
wnd1-----------|wnd1-------------|wnd0---------------|wnd1-------------|wnd0
So you always have 2/3 seconds worth of data, and on average exactly 1 second
worth of data.
The problem is the delay in getting data, which can be big for the minute-
and hour-based statistics. Suppose you have a spike that lasts 10 seconds,
it might not show in the minute-based statistics for as much as 30 seconds
after it ends (the window switches every 40 seconds).
For min/max you could return min(min0, min1) and max(max0, max1). Only the
average has this problem.
Exponential smoothing doesn't have this problem. IIRC uptime uses that.
Paolo
