[rrd-users] Can I get a single update into an RRA?

Tobias Oetiker tobi at oetiker.ch
Sat Dec 12 00:02:28 CET 2009

Yesterday David Mitchell wrote:

> I have a problem I've run into with some statistics I'm trying to
> gather. I am getting wireless client statistics from all of my access
> points via SNMP and putting the values into RRD files. All of my values
> are GAUGE's. Specifically, connection quality (S/N ratio basically) and
> connection time. I keep one RRD file per client per access point. I
> create a directory for each client MAC, and in that directory I have an
> RRD file for each access point the client has shown up on.
> The problem I run into is that some clients are connected so
> sporadically that I rarely get two updates in a row so nothing ever
> makes it into my RRAs. I can increase the heartbeat to increase the
> chances that the client will get picked up twice in the same RRD file.
> That helps, but I do end up with fictional values in the RRA making it
> appear that the client was connected for a period of time when it
> wasn't. For the most part, these clients end up with RRD files with
> recent 'lastupdate' times but no actually data in the RRAs.
> Optimally, it would be nice if there was some configuration using
> RRA:LAST or something which would result in the RRA getting populated
> with a single update. I thought about trying to fudge it by creating the
> RRD's with an extremely small step size (like 1 second) and always
> pushing two updates (N:5 -3:5 for example) at once to try and force data
> into the RRAs. It seems like there should be an easier way though.
> I'm using version 1.3.1 currently because it's in Debian stable. If
> newer versions have changed the behavior in a way which helps my
> situation, I can install a newer version. Thanks in advance,

Instead of


rrdtool update ${t}:x


rrdtool update (${t}-${step}):U
rrdtool update ${t}:x


> -David Mitchell

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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