[rrd-users] ERROR: illegal attempt to update

[David Eisner]

Tobi,

I think you must be correct.  I rewrote the Python script in C (using
system(3)), and I don't have the problem anymore. Thanks.

-David

On Sat, Jan 15, 2011 at 5:43 AM, Tobias Oetiker <tobi at oetiker.ch> wrote:
> 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
>



-- 
David Eisner     http://cradle.brokenglass.com