[rrd-users] Question about RRDTool ..
linux at thehobsons.co.uk
Thu Mar 20 08:59:06 CET 2008
Jean-Yves Avenard wrote:
>Unfortunately, this doesn't seem to work properly.
>For a start I recorded the maximum and minimum value aren't correct,
>they are rounded.
>Like the maximum in my case should be 1267.13 but it shows as 1266
>on the graph.
>rrdtool fetch speed.rrd AVERAGE
>timestamp local remote
>1205895600: 1.2642200000e+03 1.6115000000e+02
>1205906400: 1.2642200000e+03 1.6115000000e+02
>1205917200: 1.2642200000e+03 1.6115000000e+02
>1205928000: 1.2642200000e+03 1.6115000000e+02
>1205938800: 1.2642200000e+03 1.6115000000e+02
>1205949600: 1.2642200000e+03 1.6115000000e+02
>1205960400: 1.2642200000e+03 1.6115000000e+02
>1205971200: 1.2661600000e+03 1.6115666667e+02
>1205982000: nan nan
>1205992800: nan nan
>I ran manually the command:
>rrdtool update /var/www/html/adslstats/speed.rrd 1205974800:1267.13:161.16
>so where is my 1267.13 ??
>Then, in the graph itself, the line stop at what is 11AM.
>Did I miss anything in the create of the round robin database? Did I
>just misunderstand something in the documentation (I did read it over
>and over to make sure I didn't make a stupid mistake).
1205974800 is not a multiple of your interval period, therefore
normalisation WILL be done on the data and you will NOT get out
exactly the same values you put in. Go to the rrd website and look up
the tutorial on normalisation.
Your graph will stop at the last completed sample period. According
to your mail headers, you are in timezone +11, so 11am is a multiple
of 3 hours UTC. As your later email shows, when another 3 hour sample
period is complete, the graph will include it. If you want better
resolution then you need to store data at a better resolution.
Lastly, it's a good idea to explicitly round your graph end time to
be exactly on the end of a step boundary, and your start time to be
exactly an integer number of steps before the end. Under some
circumstances, rrdtool will choose a lower resolution of data for
plotting if it fills more of the graph.
>I created my RRD database like this:
>rrdtool create speed.rrd -s 10800 \
>So I have the average, min and max value collected as follow:
>data collected every 3 hours (10800 seconds)
>for 1 year (2928 x 3 hours = 366 days)
>sampled over 1 day (8 records) kept for 31 days
>sampled over 1 week kept for 5 weeks
>sampled over 1 month kept for 12 month.
Lastly, you are missing the point of rrds consolidation functions
here. Normally, the issue is that you don't want the storage overhead
of storing high resolution data over a long period - hence you would
store high res data for only a few days, medium res data for a few
weeks, and low res data for a year or two. In this case, you are
storing your highest resolution data for a full year - so there is
little point storing the other rras.
You do NOT have to store the 3 hours data for the full year in order
to have the other consolidations available.
The only gain you get here is that by carefully selecting your
graphing periods/sizes, you can avoid query-time consolidation of the
data and improve graphing speeds. Since you aren't even specifying
start and end times, you certainly aren't taking advantage of this
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