[rrd-users] MAXing or AVERAGing 1 steps

Bradley Urberg Carlson bradley at onvoy.com
Sat Jul 15 00:44:02 MEST 2000

I wanted to keep a log of exactly how many modems are in-use, with
one-minute samples.  I thought I'd put it into and RRD to make it easy to
graph (instead of using gnuplot or something).  I made a simple rrdtool

 create foo.rrd --step 60 \
 DS:modems:GAUGE:600:0:24 \
 RRA:AVERAGE:0.5:1:3600 \
 RRA:MAX:0.5:1:5760 \

When I dump the data with "AVERAGE", ...I get:

 963600900:         15.25
 963600960:         15.43
 963601020:         14.32
 963601080:         15.35
 963601140:         15.62

There were probably not 15.62 modems in-use at 963601140.  
When I fetch the data with "MAX", I get:

 963612780:         14.00
 963612840:         14.00
 963612900:         14.83
 963612960:         15.00
 963613020:         15.00
 963613080:         15.00

Similarly probably not 14.83 modems in-use at 963612900.

I thought that the "RRA:AVERAGE:xff:1:whatever" would cause "update" to
store an "average" of a group of 1 samples (therefore no averaging at
all), and the data in the log would match the "update" values exactly; and
similarly for MAX:xff:1:whatever .

I can certainly just store the values in a log-file for such a simple
purpose; but it would be good to know what's going on here, since we work
on the assumption that the AVERAGE:xff:1 RRA contains the unchanged values
that were stored with "update".


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