[rrd-users] Re: Adding "0" instead of nothing when there's no data

[Alex van den Bogaerdt]

On Wed, Sep 18, 2002 at 05:35:21PM +0200, Rejo Zenger wrote:

> I have therefor setup an extra channel on my newsserver creating a batch
> with an entry like "nl.foto,nl.markt.elektronica 1660" for every posted
> article (number is bytes of article). This batchfile is flushed every
> minute by a script run from cron. This script counts all the entries
> for every group and summarizes the bytes. In the end the script updates
> the rrd files for every group.

amount of articles == amount of lines
amount of bytes == sum of all numbers

>      RRDs::create ("$rrd_data",
>                         "--step=60",

each PDP is 60 seconds.  Good

>                         "--start=$time_start",

Only necessary to start in the past, to include historic data

>                         "DS:articles:ABSOLUTE:50400:U:U",
>                         "DS:bytes:ABSOLUTE:50400:U:U",

ABSOLUTE: real number of {articles|bytes} divided by delta time.
Example:  you enter "6000:1200000", the resulting rates will be
6000/60 and 1200000/60.  100 Articles/sec, 200000 bytes/sec.

50400: Updates received 50400 seconds apart result in unknowns.
This is "a bit" high.  What do you try to achieve?

U:U   no minimum, no maximum

>                         "RRA:AVERAGE:0.5:1:600",

600 CPDs of 1 PDP per CDP  --> 600 minutes.

>                         "RRA:AVERAGE:0.5:5:600",

600 CPDs of 5 PDPs per CDP --> 3000 minutes.
At most 50% of the PDPs may be unknown and still produce a valid CDP.
The CDP will be the AVERAGE of 5 PDPs.

>                         "RRA:AVERAGE:0.5:30:700",
>                         "RRA:AVERAGE:0.5:120:775",
>                         "RRA:AVERAGE:0.5:1440:797",

and so on.

> I'm not sure if those RRA's fit my goals.

This depends on your goals.  If you want to show graphs that display
1,5,30,120 or 1440 PDPs in each pixel, you did the right thing.
This equals: 1 pixel==1 minute, 1 pixel==5 minutes, 1 pixel==30 minutes
and so on.

> - How to get these two average lines, I don't know how to compute them
>   and how to place them.

?
You already start with averages, RRDtool continues to work with
averages, your consolidation factor is averages.  You have nothing
but averages.

To show the averages in an image, use LINE1 or AREA.

> - On the preliminary graphs I have created already, the numbers to the
>   left say "<number> m". It's not clear to me where this "m" is coming
>   from. I have read the "Grpahics with some maths" section in the
>   tutorial, but still don't get it in the relation to my numbers.

That's mili.  One article in a minute results in 1/60 articles per
second which will be displayed as 16.667 mili-articles per second.

> - The averages RRDtool computes seem to be a bit to high - probably
>   connected to the previous problem.

Yup.  You expect to see 1 per minute but you get 16.667 per second.
This is the same, yet you didn't see that yet.

Try using "CDEF:perminute=persecond,60,*" and display that.

HTH
Alex

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