On Wed, May 21, 2008 at 09:35:34AM +0000, Leon Stringer wrote: > Hi, > > I've created an RRD database to store a value (server clock offset in > ms). I've created a cron job to add the value every 6 hours. As far > as I can tell the job is running correctly and getting a valid value. > However, when I run rrd fetch I get a lot of NaN values (between a > quarter and a third of values) so the generated graphs have gaps too. > > I created the file with: > > rrdtool create file.rrd -s 21600 DS:offset:GAUGE:21600:U:U > RRA:MAX:0:1:360 > > I add the data with: > > rrdtool update file.rrd N:<val> (E.g. 1.903, -0.424, etc.) > > And I query data with: > > rrdtool fetch -s -1week file.rrd MAX > > Can anyone tell me why I see NaN values instead of the values I > (think!) am putting in?
Short answer: because you are using timestamp "N" and heartbeat 21600. Longer answer: When you run your script, it is not exactly 00:00, 06:00, 12:00, 18:00. Sometimes the interval between two updates is a bit longer than 21600 seconds, other times it is a bit shorter. When the interval is a bit shorter, RRDtool will accept the resulting rate, when the interval is a bit longer, you(!) ask RRDtool to skip that rate. Choose: 1: use fixed timestamps 2: allow for some slack (increase your heartbeat) -- Alex van den Bogaerdt http://www.vandenbogaerdt.nl/rrdtool/ _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
