[rrd-users] cant get to understand described normalization behaviour

[Peter Thurner]

Sorry, the 5 minutes were the one hour plus from utc.

For the record, this can be 'fixed' with the following:

blue at machine:~/test$ sudo ln -sf /usr/share/zoneinfo/Europe/Berlin
/etc/localtime
blue at machine:~/test$ date
Wed Mar 26 11:15:22 CET 2014
blue at machine:~/test$ sudo ln -sf /usr/share/zoneinfo/UTC /etc/localtime
blue at machine:~/test$ date
Wed Mar 26 10:15:28 UTC 2014

thank you for your help!


On 03/26/2014 09:58 AM, Peter Thurner wrote:
> perfect explaination! thank you very much!
> 
> last thing I dont get is the fact that all the data now is moved by 5
> minutes to the right or so..
> 
> I attached the new, fixed script.
> 
> 
> 
> 
> On 03/26/2014 10:47 AM, Alex van den Bogaerdt wrote:
>> I think you're missing the fact that RRDtool uses timestamps based on UTC.
>> When you specify "--step 86400" you are telling RRDtool to create a database 
>> with start and end times which are a whole multiple of 86400 seconds.
>>
>> Your first timestamp is 1395140400 which is n*86400+39600.
>> Your second timestamp is 1395226800 which also is n*86400+39600.
>> I did not check the rest but I can safely assume the rest will not be 
>> different.
>>
>> Normalization massages the input so that it fits in (n-1)*86400 to n*86400 
>> time intervals.
>>
>> The rate computed at 1395226800 is valid partially in the interval upto 
>> 1395187200 and partially thereafter. To be precise, (86400-39600)/86400 
>> stays in the timeslot computed for 1395187200 and 39600/86400 goes to the 
>> next timeslot.
>>
>> Your next update is at time 1395313200. Now there is enough data to compute 
>> the timeslot between 1395187200 and 1395273600. The rate logged at time 
>> 139573600 should be 39600/86400 * 3 + 46800/86400 * 2 = 2.458333....
>>
>> HTH
>> Alex
>>
>>
>> ----- Original Message ----- 
>> From: "Peter Thurner" <p.thurner at heinlein-support.de>
>> To: <rrd-users at lists.oetiker.ch>
>> Sent: Wednesday, March 26, 2014 10:24 AM
>> Subject: [rrd-users] cant get to understand described normalization 
>> behaviour
>>
>>
>> Hi guys,
>>
>> I'm kind of dying on this one. I attached 3 bash scripts that show where
>> I don't understand things anymore. I guess its quite simple.
>>
>> I feed the same values using the same CF and RRD specs everywhere, but
>> on the script rrdtest-days.sh, I get a graph that is a lot different to
>> the other two scripts.
>> Other than the --step size I did not change much (as a diff would show).
>>
>> Why (and how?) is it normalizing when all I increase is the timespan
>> between updates? I'm sure I missed something..
>>
>> Thank you very much in advance! :)
>>
>> Peter
>>
>>
>>
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