DEF problems with start/end time overrides

[davis3792]

Before moving up to Cacti, I was hoping to have a decent grasp on rrdtool. But I've run into a road block that I've been unable to overcome.

According to the rrdtool graph man page:
======================================
DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>]

....The time span of this data is the same as for the graph by default, you can override this by specifying start and end."
======================================

Has anyone successfully implemented the start/end time feature of DEF? I'm using Perl on XP. I've also tried straight command line and get the same results. Seems like the DEF start/end times are basically ignored - although if you put something bogus in the time spec, rrdtool complains, so it's certainly not being ignored wholesale.

Any assistance would be much appreciated...
Thanks

[TheWitness]

Both the timespan selector and the zoom features alter start and end time for the entire graph. This default behavior may negatively impact what you would like to do with your graphs.

This is the setting that would have to be over written from the rrdtool graph function:

[-s|--start time] [-e|--end time]

TheWitness

[TheWitness]

Upon futher investigation, you may be in luck:

This command fetches data from an RRD file. The virtual name vname can then be used throughout the rest of the script. By default, an RRA which contains the correct consolidated data at an appropriate resolution will be chosen. The resolution can be overridden with the --step option. The resolution can again be overridden by specifying the step size. The time span of this data is the same as for the graph by default, you can override this by specifying start and end. Remember to escape colons in the time specification!

http://people.ee.ethz.ch/~oetiker/webto ... ta.en.html

The next question, how do you place these timespans in the DEF's. Certainly, the database does not currently provide a timespan override. This would have to exist in the GRAPH TEMPLATE or GRAPH creation page for the specific Data Sources. Sounds interesting though.

I can see a month to month overlay being somewhat interesting. If you need this as a feature, please goto http://bugs.cacti.net and add a feature request. In that feature request, please be specific as to WHY you want this feature. (aka Use Case). You can also follow-up here just to let me know you have done so.

Thanks,

TheWitness

[davis3792]

ok...I'll do that...

What I want to do is to create a graph that (for instance) plots the current month AND last month on the same graph.

Any chance you or someone else could run a quick test with rrdtool to verify that the override actually works? I've spun it every way I can think of to no avail...

I'm about to the point of downloading the source to a unix box, compiling it with symbols and running it under a debugger.

[TheWitness]

Once you think you have the graph syntax right, you should be able to redirect the output to a static PNG file and compare. If the graph looks correct, then you should wave the flag ans say something like 'Yea, it works'. Then, we can work on making this fit inside of Cacti.

TheWitness

[davis3792]

The start/end times on the DEF statement are ignored if they're outside of the time range specified at the top level (rrdtool graph). And since the time range defaults to one day ago until now, any time window specified on the DEF statement prior to one day ago is ignored.

So I think the lesson is that if you use the overrides on the DEF statement, you still need to specify the time range at the global level.

Haven't found a way to show multiple time periods on the same graph yet (compare this month's CPU utilization to same time last year).

[TheWitness]

Keep us posted on any developments relative to this support.

TheWitness