Zenoss中的RRD图显示了较大时间范围内的NaN

Question

I am trying to create COMMAND JSON datasource to monitor some values, for example from such script:

print json.dumps({
    'values': {
        '': {'random': random()},
    },
    'events': []
})

And when i just starting zencommand, appropriate rrd file is created, but cur, avg and max values on graph shows me NaN. That NaNs is replaced by actual numbers when I zoom in to a current point in time, which is not very far from start of monitoring.

Why it don't show correct min, max and avg values before I zoom in? Is that somehow related to consolidation? I read http://www.vandenbogaerdt.nl/rrdtool/min-avg-max.php , but that page don't tell anything about NaN values.

And is any way to quicker zoom in to the current timestamp to see some data faster?

Answer 1

When you are zoomed out, you'll be looking at the lower-granularity RRAs (Round Robin Archives). These do not get populated until enough data are in the higher-granularity ones; so, for example, if you have a 5min-granularity RRA, a 1hr-granularity RRA, and a 1day-granularity RRA, and have collected data for the last 45min, then you will see ~8 data points in your 'daily' graph (which uses the 5min RRA), but nothing in your 'monthly' (which will use the 1hr RRA) or your 'yearly' (which uses the 1day RRA).

This applies to any RRA; AVG, LAST, MAX, etc. Until the consolidated time window is complete, and the full complement of Primary Data Points has been collected for consolidation, the consolidated data point value is undefined.

RRDTool picks the RRA to use based on the requested graph data width and pixel width, as well as the requested consolidation functions. Although there are ways to force RRDtool to use a higher-granularity RRA than it needs to, and to consolidate on the fly, this is inefficient and slow. It also makes having the lower-granularity RRA pointless and throws away one of the major benefits of RRDtool (that it performs consolidation at update time making graphing faster)