[rrd-users] graph step boundary selection algorithm

[Rafal Gwizdala]

Hi, I'm experimenting with varying graph step sizes (for auto-selecting an
optimal step size for selected date range) and would like to know what
algorithm rrdtool uses for selecting step boundaries.
For example, when I'm drawing a graph with 1 hour step (3600) then rrdtool
makes the step begin at full hours. The same with 30 minute steps, 5 minute
steps etc - every time the step boundary is adjusted to the clock time in a
reasonable  way. But for step size equal to 6 hours rrdtool makes the step
begin at 2AM, 8AM, 2PM and 8 PM instead of 12AM, 6AM, 12PM and 6PM - so
there's an overlap between days. Do you know why? Does it depend on rrd
start date, or something else?

Best regards
RG
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