[rrd-users] Calculating Max Values from multiple sources.

[Kirill Ponazdyr]

Hi,

I have a problem here, which as far as I can see is not resolvable by
RRDTOOL, but still I would like to ask before I go and look for a way
around:

Imagine that I have 4 fields in RRD Database, the data is saved with the
resolution of 1 minute, here are the 5 readings (5 Min Data)

Field		R1	R2	R3	R4	R5
---------------------------------------------------
a		3	23	7	11	0
b		5	14	13	1	2
c		32	26	0	4	8
d		4	11	2	8	0

I want to graph MAX percentage which the field "a" makes out of sum of all
fields, formula is easy:

CDEF:total:=a,b,+,c,+,d,+
CDEF:percent:a,total,/,100,*

And this formula will work well if the data is shown in a native
resolution, the plot here will be (Numbers round up):

6.8 31 31.8 45.8 0

Now I want to plot data at lower resolution, that is: one pixel equals 5
minutes, but I still want to see the MAX which was ever reached during
those 5 minutes in one pixel, that is I want my pixel to be set to 45.8 in
this case.

Unfortunately as far as I understand what RRDtool will do is take maxes of
all fields during this period and calculate a final value out of those
values:

a:23, b:14, c:32, d:11

Which will result in a pixel value of: 28.7.

Is there a way around this problem, besides of feeding precalculated "a"
value into rrd database (Unfortunately quite a PITA in our case).

Regards

Kirill


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