[rrd-users] LAST of CDEF that converts NaN to 0 always 0

[Tobias Oetiker]

Hi Matthew,

there is a 'bug' in rrdtool graph, where it fetches one 'step' more
data than is visible in the graph. This data is often 'nan'.

The LAST vdef shows you the last non NAN value. In normal operation
this works fine, but if you first convert all NAN values to 0, LAST
will show you zero since the last fetched value which was NAN was
turned into zero.

anyway, I have fixed this problem in svn, in the next release of
1.2.x as well as 1.3.0 it is fixed, so that even when you turn nan
to zero, you will get the last value visible on the graph.


see http://oss.oetiker.ch/rrdtool-trac/changeset/1386

cheers
tobi

Today Matthew M. Boedicker wrote:

> I have a DS x. I create a CDEF xz that is x with all NaN converted to 0. When
> I use a VDEF to print the LAST of x it looks ok, but the LAST of xz is always
> 0. If I graph a line of xz it looks fine. Does anyone know why this is
> always 0 or another way I can do this that will work?
>
> rrdtool create test.rrd \
> --start 1212566513 \
> --step 3600 \
> DS:x:GAUGE:7200:U:U \
> RRA:AVERAGE:0.5:1:720
>
> rrdtool update test.rrd \
> 1212570113:100 \
> 1212573713:50 \
> 1212577313:25 \
> 1212580913:75
>
> rrdtool graph test.png \
> --start 1212566513 \
> DEF:x=test.rrd:x:AVERAGE \
> CDEF:xz=x,UN,0,x,IF \
> VDEF:xlast=x,LAST GPRINT:xlast:%lf \
> VDEF:xzlast=xz,LAST GPRINT:xzlast:%lf
>
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>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten
http://it.oetiker.ch tobi at oetiker.ch ++41 62 213 9902