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

David Mitchell mitchell at ucar.edu
Fri Dec 11 17:42:11 CET 2009

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,

-David Mitchell

| David Mitchell (mitchell at ucar.edu)       Network Engineer IV  |
| Tel: (303) 497-1845                      National Center for  |
| FAX: (303) 497-1818                      Atmospheric Research |

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