[rrd-users] Fetch the time of the first entry

Alex van den Bogaerdt alex at vandenbogaerdt.nl
Wed Jul 2 12:43:36 CEST 2014

> Steve Shipway <s.shipway at auckland.ac.nz> wrote:
>> You seem to be misunderstanding how RRDTool works.
>> Remember that, after every update of an RRA, the oldest value is thrown
>> away to make room for the new one.  So, the 'first' time (the timestamp
>> of the oldest bucket in the RRA) will increase every time you update, as
>> the last bucket is thrown away.
>> Also, the 'first' value is the oldest bucket, *whether or not it has
>> been filled*.
> As I pointed out, it looks like the documentation is a little misleading
> on this. Where teh database has been filled and old data thrown away then
> the documentation is correct - but in the OPs case, it's misleading by
> talking about the "first data sample entered" into the RRA.

I briefly skimmed the source and there does not seem to be code there to
skip NaN values at the beginning. This would probably be easy to add.

It would however introduce an incompatibility for those currently using
"rrdtool first" and depending on its current behaviour.

The other option is to modify the documentation to match the source.

Burton Strauss, please chime in.

For the topic starter: "rrdtool first" and the graph command
"VDEF:datasource,FIRST" have nothing to do with eachother and are not
implemented by the same person.

More information about the rrd-users mailing list