[rrd-users] Tutorial Question

Tobias Oetiker tobi at oetiker.ch
Sat Jan 8 08:27:45 CET 2011


Today Alex van den Bogaerdt wrote:

> > Today Steve Shipway wrote:
> >
> >> I think the tutorial was written for RRDTool 1.3 or earlier, in
> >> 1.4 the fetch behaviour changed slightly to take the 'fence post'
> >> from the other end... so the tutorial needs updating.  Tobi can
> >> probably give a more precise answer...
> >
> > fetch gives you data to cover the time range you requested and then
> > some ... the 'some' bit has changed over the releases, but the
> > principle is always the same ...
> I believe the "and then some" should only be applied when necessary, and I
> don't see any reason in the case at hand?
> Both start and end time can be matched exactly, there is no graph (it is
> "fetch", not "graph") so there is no need for extra data.
> Providing one extra row "just to be sure" is not the same principle. It is
> different, unnecessary and not what the user asks nor he wants.

I have not looked at the exact data the user had, but the problem
is subtle, in the sense that if you ask for data from

-start 10 to -end 20

I have to give you

20: x
30: y

20 holds data from 10 up to 20 excluding 20 itself
30 holds data from 20 up to 30 excluding 30 itself

and since you asked for the data to end at 20 it could mean that
you could be expect to have data for 20 ...

in any event, the message is, fetch gives you enough data to cover
tha time range you asked for ...


Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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