[rrd-users] trying to understand the relationship between source data, what's in rrd and what gets plotted

[Alex van den Bogaerdt]

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.

(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):
    DEF:MyValMin=my.rrd:minrra:...
    DEF:MyValMax=my.rrd:maxrra:...
    CDEF:delta=MyValMax,MyValMin,-
    AREA:MyValMin
    AREA:delta#FF0000:values:STACK
  (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.

HTH
-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/