Getting fractions when graphing integers?

nellson · Post by **nellson** » Tue Jun 10, 2008 8:17 am

The OID I am graphing is always a positive integer from 0 - 500, as it is VPN connections to a Cisco ASA.

Yet my graphs show decimal fractions of users logged in (the Current Connections) Is there something special I need to do in teh setup of the data template to insure that it's always treated as an interger? It started as a GUAGE, but I tried ABSOLUTE and wiated a few poll intervals and saw the same behavior. .844 users logged in.

When I use getif to watch teh same OID along side Cacti, it's only an INTEGER result.

Nick

dus001 · Post by **dus001** » Tue Jun 10, 2008 8:55 am

You should check the rrdtool documentation: there is some interpolation done, if i remember correctly:
-> when a 2nd value is stored after 310 seconds, rrdtool estimates the value it was at 300, based on the 1rst one and the 2nd.

Anybody can confirm this ?

nellson · Post by **nellson** » Tue Jun 10, 2008 9:56 am

Ahh, so this is actually being turned to a decimal by RRD Tool? I could see that for an AVERAGE value, which I disbaled. I figured on an interger only dataset like VPN Connections, having the MAX and the Current would be all the was useful. Max acting like the highwater mark, and current was the valure read during that polling instance.

So might this be a limitation of RRD then? I remember my MRTG graphs of this type of thing (not using RRD) being very crisp square wave looking output on VPN Connections. Looking back at my history now with Cacti, it does look very analog over time, which doesn't look very nice. (As in the last 12 hours I reached a high of 3.2 users, when it would be nice to see it snap right to the 4.0 line where it should have been)

Any thoughts on this? Others graphing VPN connections seeing this same thing? (or did I just set my graph up wrong?)

Post by **gandalf** » Wed Jun 11, 2008 2:57 pm

dus001 wrote:You should check the rrdtool documentation: there is some interpolation done, if i remember correctly:
-> when a 2nd value is stored after 310 seconds, rrdtool estimates the value it was at 300, based on the 1rst one and the 2nd.

Anybody can confirm this ?

Confirmed
Reinhard

nellson · Post by **nellson** » Wed Jun 11, 2008 5:33 pm

Thanks Gandalf,

So this would be because the 5 min sweep went past 5 mins on this device (310 secs or longer). Would that be a behavior I can control (disable)?

Nick

nellson · Post by **nellson** » Wed Jun 11, 2008 6:22 pm

In further research, I found this:

http://osdir.com/ml/db.rrdtool.user/200 ... 00091.html

I am looking into how Cacti could apply this to my data template.

Nick

nellson · Post by **nellson** » Thu Jun 12, 2008 9:06 am

I talked with Tobi on the RRD-Tool list about this. The graphs I was getting from MRTG that showed a more square wave interger only graph of VPN Users was an artifact from a mis-use of what MRTG was for.

It looks like RRDTool is doing what it was designed to do. My question is does Cacti have alternative ways of displaying graph data other than RRD-Tool, where data sets like "Users online" that need to remain integer in the output could be rendered?

Nick

Post by **gandalf** » Sat Jun 14, 2008 1:41 pm

I followed your discussion with Tobi. Cacti as an rrdtool frontend does what rrdtool allows to do (at least most of it). Not more, sorry
Reinhard

nellson · Post by **nellson** » Sun Jun 15, 2008 10:25 pm

Thank you for the reply Gandalf,

At least now I know a lot more about how RRD Tool works, and where it stands with Cacti.

I have seen plug-ins for Cacti to do other things.. might there be any thoughts on giving Cacti alternate methods of displaying collected data?

Nick

Antoine Musso · Post by **Antoine Musso** » Tue Jun 17, 2008 3:52 am

To graph integer values, I feed the .rrd file with a custom script that makes sure the data is updated on the 300s marks.

Cacti does not do any polling, it is just used to display the graph.

nellson · Post by **nellson** » Tue Jun 17, 2008 7:14 am

Hrmm, I though about perhaps building a "Rounding" script to parse through the timestamps and move them to exact 5 min marks. I use the cacti poller running 8 threads, no real control over when it hits my host though. It'll take a bit before I get the time to dig into it. If I come up with something that works, I'll repost.

Post by **gandalf** » Wed Jun 18, 2008 1:20 pm

Antoine Musso wrote:To graph integer values, I feed the .rrd file with a custom script that makes sure the data is updated on the 300s marks.

Cacti does not do any polling, it is just used to display the graph.

That would be the only solution that I'm aware of. Creating a tricky script that's run by the poller WILL NOT WORK.
Reinhard

Getting fractions when graphing integers?

Getting fractions when graphing integers?

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