[rrd-users] ERROR: illegal attempt to update

[Tobias Oetiker]

Hi David,

my guess is that python is not blocking for the run_cmd to complete
... and thus it is possible that the os executes the rrdtool
instances 'not in order'

cheers
tobi

Thursday David Eisner wrote:

> In an effort to grok rrdtool I've written a little python script [1]
> that calls rrdtool update to generate some synthetic data.
>
> However, when I run the script, I sometimes see errors like this:
>
> $ ./rra_test.py
> rm test_rra.rrd
> rrdtool create test_rra.rrd --start 1293857700 DS:tst:GAUGE:600:0:U
> RRA:AVERAGE:0.5:5:10
> 0 rrdtool update test_rra.rrd 1293858000:100
> 1 rrdtool update test_rra.rrd 1293858300:101
> 2 rrdtool update test_rra.rrd 1293858600:102
> 3 rrdtool update test_rra.rrd 1293858900:103
> 4 rrdtool update test_rra.rrd 1293859200:104
> ERROR: test_rra.rrd: illegal attempt to update using time 1293858900
> when last update time is 1293859200 (minimum one second step)
> 5 rrdtool update test_rra.rrd 1293859500:105
> 6 rrdtool update test_rra.rrd 1293859800:106
> 7 rrdtool update test_rra.rrd 1293860100:107
>
> It doesn't happen all the time.The sleep statements in the script are
> an attempt to mitigate the problem. If I increase the sleep time in
> the loop from 10ms to 100ms, I don't see the problem.
>
> Presumably this isn't common during "real" rrdtool use, but I'm
> curious to know why it's happening. Is there some kind of race
> condition with subsequent calls to rrdupdate interfering with previous
> invocations? If so, why?
>
> This is rrdtool 1.4.4 on Centos 5.5, i386.
>
> Thanks.
>
> -David
>
>
> [1] The script:
>
> #!/usr/bin/env python
>
> import sys
> from subprocess import Popen
> from time import sleep
>
> fname = 'test_rra.rrd'
> start_time = 1293858000
> step = 300
> npoints = 8
> start_val = 100
>
> def run_cmd(cmd):
>     print cmd
>     Popen(cmd, shell=True)
>
>
> run_cmd( "rm " + fname )
> run_cmd( "rrdtool create " + fname + " --start " + str(start_time-step) +
>          " DS:tst:GAUGE:600:0:U RRA:AVERAGE:0.5:5:10" )
>
> sleep(0.1)
>
> t = start_time
> v = start_val
> for i in range(npoints):
>     print i,
>     run_cmd("rrdtool update %s %d:%d" % (fname, t, v))
>     v += 1
>     t += step
>     sleep(0.01)
>
> sys.exit(0)
>
>
>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900