[rrd-users] CDEF, RPN and multiple calculations using paranthesis

[Gerhard Ecaroh Froehlich]

Hi,

i have some question on cdef, did not find it in the docs.

I have to sum up Oracle's cachehitratio. To get an result in percent i have to
calculate (the real world values) from snmpget:

a = consistentgets = 3314928
b = blockgets = 263352
c = phyreads = 173783

( ( 3314928 + 263352 - 173783 ) / (  3314928 + 263352 ) ) * 100 = 95 

(simplified):

 ( a + b - c ) / ( a + b ) * 100 = RESULT IN PERCENT


So to follow the tutorial with the stacks:

Step:	1|2|3|4|5|6|7|8|9| 10|11
---------|-|-|-|-|-|-|-|-|---|--
RPN:	a,b,+,c,-,a,b,+,/,100,*

0	||
1       |3314928|   
2       |3314928|263352|
3       |3314928|263352|+|
4       |3578280|173783|
5       |3578280|173783|-|
6       |3404497|3314928|
7       |3404497|3314928|263352|
8       |3404497|173783|263352|+|	# Processing with 3 in stack?
9       |3667849|437135|/|
10	|8.39|100|			# which should be wrong
11	|8.39|100|*
12	|839|				# PERCENT

This is not the expected 95%.

May be it is not possible to paranthesis this way. Am i right to work around:

CDEF:cal1=a,b,+,c,-,
CDEF:cal2=a,b,+
CDEF:fin=cal1,cal2,/,100,*

Result: "fin=95"

Surely i do not fully understand the capabilities of rpn. Help is greatly
appreacheated, thanks.

bye, Ecaroh


-- 
Gerhard Ecaroh Froehlich, Systemadministrator

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