Need explanation on CDEF option on RRD graph

[sabey]

I did a very simple graph, Rx and Tx. Then I add a third graph item, the total of each of those 2 data source. I use the internal special data sources: ALL_DATA_SOURCES_NODUPS but the result of this is never the summation of each data source (Rx + Tx). Can someone could give me an explanation on that?

Maybe I don't understant the CDEF function.

Thanks

[sabey]

I also saw that the total is good when I use the LAST value but in the previous example I use the Average value.

Also, someone have an idea how I can customize the CDEF to have onlyy simple think like: CDEF:cdefe=a,b+ instead of: CDEF:cdefe=TIME,1111091548,GT,a,a,UN,0,a,IF,IF,TIME,1111091548,GT,b,b,UN,0,b,IF,IF,+ \
.

Those big string come from the ALL_DATA_SOURCE_NODUPS.

Thanks

[sabey]

Ok I did some other test. I change the CDEF by my own one: CDEF:cdefe=a,b,+ and the total average value is ok. Now the issue come from the cdef generate by the hardcoded special data source ALL_DATA_SOURCES_NODUPS. By the way, ALL_DATA_SOURCES_DUPS doesnt work!