[rrd-users] Re: -s does not consolidate!

[Iain Buchanan]

Hello again,

Thanks for the help on the last question (TIME & rpn).  I realised that I
wasn't getting any pretty pictures because the time I specified wasn't large
enough to display anything on the graph.  If anyone has a better idea for
drawing dot graphs, then please let me know.

I have come accross a 'feature' of rrdtool that seems to contradict itself.
The idea of RRA's as far as I understand is to consolidate and store data,
according to some CF.  Now, I decided that instead of making my step 1 (my
data comes in every second), I would make it the equivalent of the amount of
data in 1 pixel (No. samples / width of graph) to save disk space and speed
up the graphing process.  But I noticed that all of a sudden I had lost my
maximum and minumum information.  I have 3 CF's for min max and average.
Because I get data so frequently (every second) and I want to graph it over
weeks and months, the maximum and minumum values are very important,
especially as the graphing period becomes longer.

It seems that rrd averages data that arrives more frequent than the step
interval instead of consolidating it according to the CF of the particular
RRA.  For example
--------------------
create test.rrd --start 1006612200 -s 864 DS:trend:GAUGE:112:U:U
RRA:AVERAGE:0.5:1:700 RRA:MAX:0.5:1:700 RRA:MIN:0.5:1:700

update test.rrd lots of data (one value per second for a week)

graph graph.png --start 1006612200 --end 1007217000 -w 700 -h 300 -a PNG
DEF:max=test.rrd:trend:MAX LINE1:max#FF0000:trend_max
DEF:ave=test.rrd:trend:AVERAGE LINE1:ave#0000FF:trend_ave
DEF:min=test.rrd:trend:MIN LINE1:min#88CC88:trend_min
--------------------
864 is the number of seconds in a week divided by the width of the drawing
area of the graph (700).  I have tried different values for step and steps
and the result is still the same.

Thanks in advance,
Iain.



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