On Mon, Sep 15, 2014 at 01:13:08PM +0200, Markus Armbruster wrote: > Benoît Canet <benoit.ca...@nodalink.com> writes: > > > On Mon, Sep 08, 2014 at 05:09:38PM +0200, Paolo Bonzini wrote: > >> 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. > > > > I am writing this so cloud end users can programatically get informations > > about > > their vms disk statistics. > > > > Cloud end users are known to use their cloud API to script the > > elasticity of their > > architecture. > > Some code will poll system statistics to decide if new instances must > > be launched > > or existing instances must be pruned. > > This means introducing a delay in the accounting code would slow down their > > decisions. > > > > min and max is also useful to know since it gives an idea of the deviation. > > For what it's worth, the algorithm in the Dr. Dobb's Paolo referenced > can compute a standard deviation. Can we figure out what users really > want, standard deviation, min/max, or both?
My test subject think that min/max convey more information than standard deviation and that anyway the second can be computed with the formers. Does Red Hat have other tests subjects at hand ? Best regards Benoît > > [...]
