On 21.04.2013, at 10:43, Oliver Loch <grime...@gmx.net> wrote:
> HI,
>
> Am 20.04.2013 um 11:17 schrieb Alex van den Bogaerdt <a...@vandenbogaerdt.nl>:
>
>> Please just do some experiments with fake data.
>>
>> Create two databases with the same property, ABSOLUTE counter type. Update
>> them using the same timestamps (do not use "N"), four times a second, and
>> make sure there is enough data to fill a couple of timeslots in your RRA.
>
> Using the same timestamp again gives me an error. This is what I did:
>
> Wrote a script:
>
> #!/usr/bin/env bash
>
> set -x
>
> file=test.rrd
> ts=$(date +%s)
>
> rrdtool create test.rrd -s 1 DS:gpio0:ABSOLUTE:14400:1:15000
> RRA:AVERAGE:0.5:60:500
>
> for i in {1..3}; do
> rrdtool update test.rrd ${ts}:3600;
> done
>
> and then executed it, with the following results:
>
> root@LePi:~/tests# ./ts
> + file=test.rrd
> ++ date +%s
> + ts=1366557702
> + rrdtool create test.rrd -s 1 DS:gpio0:ABSOLUTE:14400:1:15000
> RRA:AVERAGE:0.5:60:500
> + for i in '{1..3}'
> + rrdtool update test.rrd 1366557702:3600
> + for i in '{1..3}'
> + rrdtool update test.rrd 1366557702:3600
> ERROR: test.rrd: illegal attempt to update using time 1366557702 when last
> update time is 1366557702 (minimum one second step)
> + for i in '{1..3}'
> + rrdtool update test.rrd 1366557702:3600
> ERROR: test.rrd: illegal attempt to update using time 1366557702 when last
> update time is 1366557702 (minimum one second step)
> root@LePi:~/tests#
>
> So using the same timestamp multiple times per second doesn't seem to work
> for me.
you must use high precision timestamps
3.1:5544455
3.2:765577
3.543:6645667
cheerst tobi
>
>> Feed 3600 into one RRD every time, feed 1 into the other RRD every time.
>>
>> You should see a rate of 14400 in the first, and 4 in the other.
>>
>> Now use a CDEF to multiply 4 by 3600, and you get 14400 again. Same
>> resulting rate, other way to achieve it. The resulting databases have
>> Joules/second in the first, and Wh per second in the other. That CDEF
>> transforms Wh into J, because 1 Wh is just 3600 J.
>>
>> Do not confuse this with another reason to multiply by 3600. You have been
>> asking about 'per hour' rates. If you have 1 Wh per second, constantly, then
>> after an hour you will have used 3600 Wh. So if you multiply a rate by 3600,
>> you get 'rate per hour' instead of 'rate per second'.
>>
>> If your database contains Wh, and you want to know Joules/hour, then you
>> need to multiply by 3600 twice (or one time by 12960000, for performance
>> reasons).
>
> The joules thing is something you started to talk about. Not really my
> problem. And I know that I get 3600W/h when I have one watt/hour per second.
> Its simple math, but at the moment it doesn't seem to be possible to update
> multiple times per second.
>
>
>> And to answer your question about where RRAs get their data: it is already
>> described. PDPs are used to build CDPs. See the three phase description
>> again. If RRAs get their data from other RRAs, it would have been described
>> there.
>
> So just for my understanding: If I want to have an RRA that holds the daily
> average of the power consumption over a month, I need to create an rrd with
> 86400 PDPs? And If the average should be covered on a weekly basis over a
> month, I'd need an RRD with 7*86400 steps and it needs to be created like
> this:
>
> rrdtool create test.rrd -s 1 DS:some-input:ABSOLUTE:14400:1:15000
> RRA:AVERAGE:0.5:604800:52
>
> ?
>
>
>> Really, you are thinking and assuming a lot, but you do not verify this by
>> experimenting.
>
> I'd prefer verifying things with the help of documentation. And I'm not
> assuming anything, I'm asking how something could be done and present an idea
> I had to verify if it is possible this way. But it doesn't seem to be, so
> thanks for that.
>
>> Start simple. Step==60 (meaning: every step is 60 seconds). Update with
>> timestamps that are a whole multiple of 60 (n*60). Start simple with three
>> RRAs, one using 1 PDP per CDP, one using 2 PDP per CDP and one using 3 PDP
>> per CDP. See what happens, and when it happens, by examining the resulting
>> RRD every time between updates.
>>
>> Later you start updating with timestamps that are not a whole multiple of 60
>> seconds, e.g. at n*60+10, and you learn about normalization.
> I know how normalization (standard score) works. It's not black magic to me.
> But the question if writing multiple values to the database per second then
> leads to a max value in the PDP or to the average in the PDP (yes, the PDP,
> multiple updates per second -> normalization -> PDP), hasn't been answered
> till now. Asking again then lead to your statement that it would be better to
> multiply the value outside rrdtool first and then write it to rrd.
>
> Facing the fact, that it doesn't seem to be possible to update multiple times
> with the same timestamp, I'd say that either I'm missing something (timestamp
> with mili-/microseconds perhaps?) or that something else doesn't seem to
> work. Again: that's why I'm asking for it here.
>
> Thanks.
>
> KR,
>
> Oliver Loch
>
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