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

[Alex van den Bogaerdt]

On Wed, Sep 21, 2005 at 07:51:57PM -0500, christian smyth wrote:

>         http://www.fuzzy-elves.org/rrd/

I've copied the data and performed some tests myself.

The problem seems to be in the amount of detail on the Y-axis.  When I
run your data through a for-next loop, using both of your graph commands,
I to see a huge difference.  I got times between 0.6 and 12.1 seconds.

Then I tried something,  I added a CDEF to the scripts, effectively destroying
your data and plotting some random value.

"CDEF:val2=1,val1,POP"
costs about 0.6 seconds (on my slow computer this was as fast as it gets) and 
"CDEF:val2=50000000,val1,POP"
took twice as much time (still not very much).

Really interesting was:
"CDEF:val2=PREV,1,EQ,50000000,1,IF,val1,POP"
which I amost aborted because it took so much time (56 second per graph).


So, as the difference on the Y-axis seems to be important, I tried this:
"CDEF:val2=val1,1024,1024,*,/"
which didn't have the impact I expected it to have (none, to be precise).

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?


I really should be doing other things right now so this will be it for today.

HTH
Alex

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