Re: [pcp] Floating point problem

[Ken McDonell <kenj@xxxxxxxxxxxxxxxx>]

On 31/07/14 08:00, Brendan Gregg wrote:
> ..
>
> I actually like 2. It's simple.
>
> I'd like to not just fetch per-second metrics, but possibly other
> intervals at the same time, including per-hour and per-day. And possibly
> from multiple clients. And possibly ad-hoc queries. With 2, I simply
> stash away whatever cumulative values and timestamp pairs, and use them
> later when needed.
Excellent.

2. is more consistent with the PCP philosophy where rate conversion 
(which is but one form of aggregation) is preferably the domain of the 
clients consuming the performance data, rather than the producers of the 
data.
You'll need to stash the timestamps from the fetches also to do the rate 
conversion (or other temporal averaging) based on the consistent 
timestamps at the source of the data.
If you start to do serious aggregation, you'll also need the metadata to 
know if a metric is a counter or not and to allow correct scaling, e.g. 
to get the units of time for the CPU metrics, so you can scale as 
required before dividing by the delta in the timestamps.
This has all be done before (as Frank points out!), so lemme know if you 
need any assistance.