[rrd-users] another newbie question (sorry this is kind of long)

Steve Shipway s.shipway at auckland.ac.nz
Sun Nov 13 22:00:49 CET 2011

> So, as you can see, I'm not doing anything too crazy.  What I'm
> confused about is that when I read the data back from the database via
> a perl script (or via rrddump), it is not showing up as an integer.  I

Welcome to the most frequent of frequently asked questions.

This is known as DATA NORMALISATION and is a standard feature of RRDTool.  When graphing network traffic (the original use of RRD) it is great; if you think of RRD as a traditional database that stores exactly what you're given, it is not.

http://rrdtool.vandenbogaerdt.nl/process.php This is the best explanation of what's going on and why.  In short, RRD is adjusting your data so that the time component fits exactly on the interval boundary, and in doing so also adjusts the value under the assumption that when viewed this close it approximates a straight line.  This is only problematic if the values are small integers (eg, number of pages printed on a printer in a minute).


Steve Shipway
ITS Unix Services Design Lead
University of Auckland, New Zealand
Floor 1, 58 Symonds Street, Auckland
Phone: +64 (0)9 3737599 ext 86487
DDI: +64 (0)9 924 6487
Mobile: +64 (0)21 753 189
Email: s.shipway at auckland.ac.nz
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