[rrd-users] Re: NaN Math options

[Alex van den Bogaerdt]

Philip Molter wrote:
>                                                          If one of
> our interfaces goes down and returns no data, we get unknowns in
> our database for that time period.  When we put these unknowns into
> the sum, the graph disappears, because the entire value becomes
> unknown.
> 
> Simple enough fix, right?  You just do something like:
> 
>   DEF:int1=file1:octets:AVERAGE
>   DEF:int2=file2:octets:AVERAGE
>   CDEF:int1,UN,0,int1,IF,int2,UN,0,int2,IF,+

[...]

> What we really want is to start the graph from the interval closest
> in time to the current time.  Our last value isn't /really/ unknown,
> and it's not really zero.  Is there a way to make the graph start
> from there rather than the absolute nearest time?

Try if this helps (may need some modifications):

DEF:int1=file1:octets:AVERAGE
CDEF:int1b=int1,UN,LAST,int1,IF
CDEF:int1c=int1b,UN,0,int1b,IF
DEF:int2=file2:octets:AVERAGE
CDEF:int2b=int2,UN,LAST,int2,IF
CDEF:int2c=int2b,UN,0,int2b,IF
CDEF:sum=int1c,int2c,+

If I understand the man page correctly, the only way you'll get an
unknown in int1b is when the datasource has been unknown from the
beginning. The second CDEF is used to even prevent that unknown to pass.

Please let me know if this helps, just curious!

regards,
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