[rrd-users] trying to understand the relationship between source data, what's in rrd and what gets plotted
Mark.Seger at hp.com
Fri Jul 20 19:31:06 CEST 2007
Alex van den Bogaerdt wrote:
> On Fri, Jul 20, 2007 at 12:31:25PM -0400, Mark Seger wrote:
>> more experiments and I'm getting closer... I think the problem is the
>> AVERAGE in my DEF statements of the graphing command. The only problem
>> is I couldn't find any clear description or examples of how this works.
>> I did try using LAST (even though I have no idea what it does) and my
>> plots got better, but I'm still missing data points and I want to see
>> them all. Again, I have a step size of 1 second so I'd think everything
>> should just be there...
> Last time I looked, which is several moons ago, the graphing part
> would average different samples which needed to be "consolidated"
> due to the fact that one was trying to display more rows than there
> were pixel columns available.
Ahh yes, I think I see now. However, and I simply point this out as an
observation, it's never good to throw away or combine data points as you
might lose something really important. I don't know how gnuplot does it
but I've never see it lose anything. Perhaps when it sees multiple data
points it just picks the maximum value. hey - I just tried that and it
This may be obvious to everyone else but it sure wasn't to me. I think
the documentation could use some beefing up in this place as well as
some examples. At the very least I'd put in an example that shows a
series that contains data with a lot of values <100 and a single point
of 1000. Then explain why you never see the spike! I'll bet a lot of
people would be shocked. I also wonder how many system managers are
missing valuable data because it's simply getting dropped out off.
> (I wrote consolidated surrounded by quotation marks because it isn't
> really consolidating what's happening)
> In other words: unless your graph is 50k pixels wide, you will have
> to select which 400 out of 50k rates you would like to see, or you
> will have to deal with the problem in a different way. For example:
> If you setup a MAX and MIN RRA, and you carefully craft their parameters,
> you could do something like this:
> * Consolidate 60 rates (1 second each) into one (of 60 seconds).
> This means setting up an RRA with steps-per-row 60.
> * Display 400 x 60 seconds on a graph (or adjust the graph width,
> together with the amount of CDPs to plot).
> * Do this using (you fill in the blanks):
> (That first area does not plot anything, and it is not supposed to.
> The second area displays a line from min to max.)
> * Do the same for 3600 steps per row, and 400x3600 seconds per graph
> and so on. Of course you can adjust the numbers to your liking.
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