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

[Simon Hobson]

Steven Sim <unixandme at outlook.com> wrote:

> I intend to process a data file each day but create the rrd database on the FIRST day of the month.
> 
> The creation shall ensure sufficient data points in the first day to contain the entire month but plot daily graphs until the end of the month, whereby it will plot the entire month.
> 
> Say for example,
> 
> If i had a step interval of 15 minutes (900 seconds), 
> 
> rrdtool create $RRDB --step 900 --start $STARTIME \
> DS:......
> DS:......
> .
> .
> .
> DS:......
> DS:......
> RRA:AVERAGE:0.5:1:2880
> 
> 2880 = 24 hours x 4 data points per hour x 30 (thirty days in a month)
> 
> 4 data points since one hour has 4 data points (15 minutes step).
> 
> Would the above be correct?

Yes, your numbers are correct, but I wonder about your methodology. It might help if you said what you are trying to achieve, because it's a rather unusual way of using RRD. Normally, you simply create one RRD that collects, stores, and consolidates the data you want. Typically this means keeping high resolution data for a shortish time, and keeping progressively lower resolution for progressively longer times - eg most applications don't need to keep (say) 5 minute resolution traffic data for 2 years ago. That's not to say you can't keep several years worth of high-resolution data if you want to.

By keeping separate RRD files for each 'month', you'll find that it's hard work if you later want to do a graph for a year ! You'd also need to lock your "filled" data files otherwise one update to the wrong file could wipe out all the data.