[rrd-users] Re: rrdtool graph slow on some columns

Tobias Oetiker oetiker at ee.ethz.ch
Mon Sep 26 22:44:31 MEST 2005

Hi Christian,

I did some runtime analysis of the code and the difference between
the two versions comes from the extra time libart spends in the
art_svp_render_aa_iter_step and art_svp_intersector routines. My
guess is that this happens because in the first example renders the
horyzontal line right on a 'pixel' whereas the second example does
render it between two pixles ... so what you get is the best and
the worst case rendering compared ... you get a similar effect when
you modify the first example to draw a LINE1.5 ... not as extreem
but in the same direction ...

I'm afraid there is not much I can do about this just now ... but I
plan to move to cairo for the 1.3 series and I hope that the cairo
library will have better performance than libart ...


> On Thu, 2005-09-22 at 04:20 +0200, Alex van den Bogaerdt wrote:
> > However, the following did work:
> > "CDEF:val2=val1,1024,1024,*,/,FLOOR"
> > About 0.6 to 0.65 seconds is not bad, certainly not when compared to 12.
> > Christian, please try that yourself.  Of course you need to graph val2, not val1.
> > You could save some extra cpu cycles by changing "1024,1024,*" into 1048576 or
> > 1024000 (whichever is appropriate for you).
> >
> > Tobi, seems to me a function such as apply_gridfit() may be the cause?
> Alex,
> Far out; I get the same results you do, using my old version of rrdtool!
> Graphing val2 from your CDEF works much better than graphing val1 from
> the DEF.  It runs in virtually the same length of time as does a graph
> of one of the "fast" columns.  This seems to be a fine workaround, once
> I adjust my Y-axis label.  I like graphing in MB (maybe even GB) better
> than graphing in KB anyway.  Thanks!!!
> Tobi,
> What is your take on this?

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