Hi Chris, I assume that it has to do with different "bucket-sizes" which is a result of your different timeframes. The max-functions are working on finding the max-values in a Array of data-values.
Lest just have an example with 10 values A: 2 3 4 5 5 6 4 3 3 4 B: 6 6 8 5 4 4 3 2 1 1 If you look on each of the value - and sum that up with the same number of values - you will get: AB: 8 9 12 10 9 10 7 5 4 5 And the max of this will be 12. But when looking at a year, you may have consolidated the individual numbers into larger buckets - where the max-values are kept. Lets just create an example where two values are "joined" (timeslot increased to contain 2 values) - so we reduce the buckets to 5. Most people have maybe 2 weeks of data with full resolution, and then consolidate this to larger buckets (from minutes to hours) - and then after a few months of them - go up to some even larger buckets (hours to days). With the same max, we would then have: A2: 3 5 6 4 4 B2: 6 8 4 3 1 And our new max-array of the sum would be: AB2: 9 13 10 7 5 Where the max-value is 13 - and not 12 as above. I'm not sure what you want to accomplish. If you are trying to look on some bandwidth-numbers you should probably not use max anyway - as even a very short peak would offset your hole yearly-data. Regards, Johan On Tue, 2013-08-06 at 06:27 -0700, Chris Mason wrote: > Hi, > > > > I am trying to create a combined graph with data from two data sources > and I am seeing some unexpected results. I have removed everything > from my graph and produced a simple script which recreates the > problem: > > > DEF:A='a.rrd':DS1:MAX > DEF:B='b.rrd':DS1:MAX > > > CDEF:AB=A,B,ADDNAN > > > > PRINT:A:MAX:'A\: %.3lf %S' > PRINT:B:MAX:'B\: %.3lf %S' > PRINT:AB:MAX:'Total\: %.3lf %S' > > > If I graph this with "--start -1m" I get the following: > > > A: 749.807 M > > B: 1744.822 M > Total: 2325.624 M > > > and with "--start -1y": > > > A: 749.807 M > B: 1744.822 M > Total: 2430.266 M > > > When I attempt to display data with "--start -1y" this is where the > problem occurs. As you can see the MAX value for A and B hasn't > changed, but my total has? > > > When I convert these values into bps then the difference is 837mbps > which isn't a small amount. > > > Am I doing something wrong or is this expected? > > > Thanks, > Chris
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