[collectd] Reserved swap and Linux (was: 2 Small problems with collectd)

Florian Forster octo at verplant.org
Mon Jul 10 20:08:20 CEST 2006


On Mon, Jul 10, 2006 at 06:29:54PM +0200, Jan Huijsmans wrote:
> Isn't it possible to just log 0 instead of nan? When there is no
> reserved swapspace, a value of 0 seems to be a valid work around.

yes, it's possible. In fact, getting NaNs in there is harder, especially
with counters.

To answer the question you actually meant though: Loggind `unknown' or
`nonexistent' as NaN is a feature, not a bug. If you prefer seeing zeros
in your graph you can use a CDEF along these lines:
The file `contrib/collection.cgi' does this for drawing the `AREA's, so
you might take a peek there.

The other way around (logging zeros, finding out where the value wasn't
available) is impossible, so doing this would destroy information.

> BTW this only went wrong with new collectd setups (or ones with the
> swap file erased) With older setups I just have the value 0.

That's weird.. To get a NaN into the RRD file an invalid value (-1) is
logged. I can't imagine that was ever legal and if it was, then there
should be a negative one, not a zero in there. Just out of curiosity,
could you provide the output of `rrdtool info' for such a file?

Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
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