[rrd-users] Re: rrdtool fetch with computed resolution
linux at thehobsons.co.uk
Fri Aug 4 10:53:17 MEST 2006
Sven Ubik wrote:
>I am not sure about your question. Are you asking why I want to fetch data
>with arbitrary time resolutions?
>It is interesting to see dynamics of network characteristics in different
>timescales. RRD file can store statistics in only a limited set of time
>resolutions, which are fixed and cannot be changed later. Why not to
>compute statistics over different time resolutions than those directly
>stored in RRD files?
Lets get this clear, as I read it you want to extract data at a later
date which has a different resolution to what you have stored ?
The only way to do this is to store data covering the whole period
you may want to chart over, and at the best resolution that you will
ever want - you can't extract information later that you don't have
stored. That's likely to be a huge store, and also not what rrd is
You can make rrd do that by simply telling it to store a lot of
samples at high resolution - it will make a big rrd and take a lot of
processing to use. rrd is designed to allow you to automatically
consolidate data so that you can (typically) have high resolution
over a short time, and low resolution data over a long time,
balancing flexibility with efficiency of storage and computation.
For example, I have just set up a system that keeps network traffic
(average & max, in and out, 255 sets) with 5 minute resolution up to
2 days, 1/2hr up to 14 days, ... down to 12hour samples over 2 years.
The rrd file is already 28M and the grapher needs anything up to 800M
of memory to draw the graphs. I hate to think what the storage and
processing requirements would be for 2 years of data at 5 minute
samples ! Actually, neglecting overhead (not inconsiderable in
itself) it's something in the order of 200MB times whatever the size
of the float values is (ie a 4 byte value would require over 800MB of
Because we're never likely to be interested in the value over a 5
minute sample 8 months ago, were happy to trade off the resolution
for less storage and more importantly less processing, to produce
graphs that will give us an overview. rrd makes that almost trivial
Unsubscribe mailto:rrd-users-request at list.ee.ethz.ch?subject=unsubscribe
Help mailto:rrd-users-request at list.ee.ethz.ch?subject=help
More information about the rrd-users