[rrd-users] Rrdtool for counting irregular events
linux at thehobsons.co.uk
Mon May 21 15:07:05 CEST 2012
Rafal Gwizdala wrote:
>Or maybe the step can be calculated based on graph date range? If
>so, what's the algorithm rrdtool uses?
It should attempt to use the most detailed data that will fill the
graph most fully. If you have consolidations where every
consolidation is a multiple of the shorter ones (eg, 30mins is a
multiple of 5 mins, 2 hours is a multiple of both 30 and 5 minutes,
and so on) then this will normally mean using the most detailed data
Example, you consolidate over 5 minute intervals for one day, and 1/2
hour over one week. If you ask for a graph which starts not more than
24 hours ago, then you'll see 5 minute data. Go back a few minutes
more and you'll get 1/2 hour data as the 5 minute data won't fill the
graph. This is because there is never a situation where a lower
resolution consolidation covers a period that isn't also covered by a
higher resolution one - at least as far back as the higher resolution
Where it breaks down is if the consolidated periods are multiples of
each other. Suppose you consolidate over 2 minutes and 5 minutes.
Graph from midnight (00:00) to 00:14 and you'll get 7off 2 minutes
samples. Graph from midnight to 00:15 and you may get 3off 5 minute
samples as that will fill more of the graph.
From memory, you can force the resolution to be used - which would
result in the 15 minute graph showing the more detailed data with a
gap at the end (if you forced the 120s resolution). I also believe
some changes have been made since I last took any notice of this and
I don't know what changed.
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