[rrd-users] Re: Can't retrieve the data I put in

Alex van den Bogaerdt alex at ergens.op.het.net
Fri Sep 1 00:52:08 MEST 2006

On Thu, Aug 31, 2006 at 06:14:56PM -0400, Jason Greguske wrote:

> update it (happens every 5 minutes):
> # rrdtool update my.rrd -t trial N:34590

Update happens "N" which you assume to be every 5 minutes but may
be 299, 301, 300, 299, 300, 301 seconds apart.  You can't know
the exact time you are executing this command.

> fetch the most recent data back out:
> # rrdtool fetch my.rrd LAST -s `rrdtool last my.rrd`

Unless that time stamp happens to be exactly a whole multiple of 300,
you are requesting for data that has not yet been consolidated.

> I just want to retrieve the most recently added data, exactly as I put
> it in, but the fetch command always returns nan's. What am I missing?

You don't put data into the database.  You tell rrdtool what data
you have for rrdtool to compute a rate.  rrdtool then stores the

Yes, you are missing something fundamental.  See my site, especially
the entry "Rates, normalizing and consolidating".

Alex van den Bogaerdt

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