[mrtg-developers] Calculating 95th percentile

[Jo Rhett]

Much simpler to just do this:

CDEF:pctbits=ds1bits,ds0bits,MAX
VDEF:pct=pctbits,95,PERCENT

On Oct 10, 2007, at 9:06 AM, Westlake, Simon wrote:
> Hello all,
>
> I'm attempting to write a script to calculate 95th percentile usage
> using RRD files generated using MRTG. I'm using PHP and PHP4RRDTool in
> order to pull the information and calculate it and I'm running into an
> issue which has maybe been hidden from me in the past as I use MRTG  
> as a
> collector for my RRD files.
>
> A quick rundown of my method:
>
> I have a loop that goes through and pulls 5 minute intervals of data
> from the RRD file (by doing --start -10m --end -5m for example, and
> moving backwards in steps of 5) for the last calendar month. It adds
> this data to an array, sorts it from smallest to largest, strips  
> the top
> 5% and calculates the average.
>
> The script itself seems to work fine, but the data I get returned  
> seems
> weird.
>
> After reading the RRD documentation, it appears that I should be  
> able to
> pull the information I want by using the following command:
>
> $opts = array ( "AVERAGE", "--end", "-$timeframe", "--start",
> "-$start");
>
> Where the $opts array is an array of the options to send. This  
> works and
> gives me a value, however, the values seem to repeat identically. Here
> is a (somewhat brief) example of the data returned over a series of 5
> minute queries:
>
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 33748465.7228
> 34784619.7841
> <34784619.7841 repeats many times>
> 34784619.7841
> 34993760.8949
> 34993760.8949
> 34993760.8949
> 34993760.8949
> 34993760.8949
> 34993760.8949
> 34993760.8949
> 34993760.8949
>
> This seems wrong to me - even as an average, I would not be seeing
> identical values over separate 5 minute intervals.
>
> I have tried various changes to see if I receive different  
> information,
> and I do not.
>
> Am I missing something blindly obvious here? Shouldn't different 5
> minute intervals return different information?
>
> --
> Simon Westlake
> Time Warner Cable Business Class
> Network Engineer
> Ph: 414.908.4791 | Cell: 414.688.7956
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-- 
Jo Rhett
senior geek

Silicon Valley Colocation
Support Phone: 408-400-0550