[mrtg] Re: How much is too much?

[Bradford Woodcock]

Alex, an interesting comment lets work it through a bit mainly so I
understand mrtg's use of time.

I see your point in the calculation problem however it all depends on how
(and when) mrtg determines the time difference between polls.

>Result: MRTG will calculate a difference in time which is, for example,
>five minutes.  The actual samples were taken 4.5 minutes apart in real
>life.  

The question becomes from the comment above "How does mrtg calculate the
time difference?". Do you (or someone on the list) know the answer to this
as I haven't looked at the code?

- Does it use system time when the mrtg job *1st* executes? (least accurate
as you describe)
- Does it use system time for each router or interface as it goes through
the config? (more accurate)
- does it use sysUpTime at all and when?
- what testing has been done to determine the level of accuracy of the
metrics given varying system loads (probably only needed if using system
time at mrtg startup)?

And if there are inaccuracies there are a couple different views to be
taken depending on expectations. If the user wants perfect 5 minute
calculations then mrtg might not be the tool for the job (depending on
answers above). If you are mainly using it for trending (that would be me)
then having a level of inaccuracy isn't the end of the world given that the
trends over time will be fine. So long as it is at least within a couple
percent on individual 5 minute intervals I can live with it given that the
next value will simply lean the other way.

cheers,
brad... 


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