[rrd-users] Re: Interpreting RRD output - Maximum

[Alex van den Bogaerdt]

Lyle Brooks wrote:

> > You are consolidating averages.  The average of (1,2,3,4,5) is 3.
> > max(1,2,3,4,5) is 5 while max(avg(1,2,3,4,5)) is 3.
> 
> Ok, That I follow.  I guess I'm not understanding what the proper
> incantations are to make RRDTool do that.

This was the "use" part of

> > You need more RRAs.  They should keep the maxima.  When you're
> > going to plot and/or print maxima, use those RRAs.

Basically you don't only do
   DEF:AvgIn=......AVERAGE....
but also do
   DEF:MaxIn=......MAX.....

Then you print using GPRINT:MaxIn:MAX:...  and GPRINT:AvgIn:AVERAGE:...
and so on, but first read until the end:

> Similarly, I must be doing something wrong because all these commands
> generate the same output, which is not what I anticipated.
> 
> rrdtool fetch myfile.rrd AVERAGE -s -24hr
> rrdtool fetch myfile.rrd MIN -s -24hr
> rrdtool fetch myfile.rrd MAX -s -24hr
> rrdtool fetch myfile.rrd LAST -s -24hr

This will probably have to do with the "best-match" function inside
rrdtool.

You're asking for "now"-24h to "now".  "Now" will most likely not be
on an interval boundary and the closest match is the RRA with just
one PDP per CDP.

In other words, you are viewing:
   AVERAGE(1)
   MIN(1)
   MAX(1)
   LAST(1)
and this obviously is 1 in all cases.  Consolidation hasn't happen
yet so the results are the same.

> I've read the tutorials, and the man pages and looked through some 
> sample code, but I've clearly missed something important.

You're not using the other RRAs.

Use --end 00:00 --start end-24h and try again.  I'm confident this
will solve your immediate problem.

Now try other times for "--end" such as 00:01, 00:05, 00:30, 00:35 
and so on until you see the pattern.  Compare with the output of
rrdtool dump.

HTH
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