[rrd-users] mrtg + rrdcached

Tobias Oetiker tobi at oetiker.ch
Tue Feb 2 16:22:32 CET 2010

Hi Steve,

Today Steven Hartland wrote:

> ----- Original Message ----- From: "Tobias Oetiker" <tobi at oetiker.ch>
> > > I tried getting mrtg to work with rrdcached but it uses updatev
> > > in the rrdtool v1.2+ code path so it doesn't work. Looking through
> > > the code it seemed like there was no reason why if we forced the
> > > old 1.1 path it wouldn't work just fine.
> >
> > except for the rrdtool fetch which is necessary to figure out of
> > alarms have to be raised which would force rrdcachd to flush the
> > cache on every round ... but if you do NOT use alarms, then things
> > should work fine.
> Hmm, we don't use alarms but there doesn't seem to be any condition
> on the fetch, so its only processed if there are threshold checks
> are defined.

if there were, updatev is actually exactly as fast as update
(unless you are using the cached) and a lot faster then update/fetch ...

without looking at the code I would guess that if you have not set
any thresholds, you should be fine with update (no *v)

> Are you saying that the call to threshcheck and the info / fetch
> block under the comment:
> # get the rrdtool-processed values back from rrdtool
> in mrtg could be skipped if no threshold checks are defined?

well the info bit is done to figure if the rrd file matches the
requirements. but in daemon mode this is done only once so the
impact should not be too bad.
> The following is the stats from our rrdcached which has been running
> now ~ 30hours, it does seem to indicate there are a very large number
> of possibly unneeded flushes happening, do you think this is down
> to the mrtg fetch?

if fetch runs, then there will be flushing ...


> 9 Statistics follow
> QueueLength: 0
> UpdatesReceived: 9156170
> FlushesReceived: 1083366
> UpdatesWritten: 1475662
> DataSetsWritten: 9103092
> TreeNodesNumber: 4153
> TreeDepth: 15
> JournalBytes: 0
> JournalRotate: 0
>    Regards
>    Steve
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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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