[rrd-users] Re: [rrd-developers] rrd resize

[Alex van den Bogaerdt]

On Fri, Sep 06, 2002 at 11:08:00PM +0200, Tobias Oetiker wrote:

> Note also that rrdtool will pick the RRA which best matches the
> resolution you request when graphing or fetching ...

Which is why it is a good thing to set an explicit end time
and an explicit duration.

If the desired step size is 7200 seconds (2 hours per pixel) and
the inner part of the graph is 400 pixels, the following will do:

    rrdtool graph whatever.png --end 00:00 --start end-2880000

(2880000 is the amount of pixels times the amount of seconds per
pixel)

The RRA selection mechanism (best match) will first try to
return as much "time" as possible, then it looks at the resolution.

If one queries "--end now --start end-33d8h" and "now" is not
exactly right (read: a 2-hour boundary), the RRA with the high
resolution is a better match than the RRA with the lower resolution
is.

Before using "resize", the high-resolution RRA had not enough
rows to satisfy the request and thus the low-resolution RRA
was the better match.

cheers,
Alex

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