Hi Derek, Aug 22 Derek Haynes wrote:
> Tobias, > > > in any event, on a technical level, what would be required to > > achieve what you want (appart for the handling of unknown periodes > > within a single step) would be an AVERAGE_UNKNOWN_AS_ZERO > > consolidation function ... this would not break the assumptions > > about the nature of RRAs and you could calculate your type of SUM > > easily ... > > Makes sense. > > > a + unknown = a > > This seems to have been addressed in other areas (ADDNAN / TOTAL > w/VDEF) both appear to treat unknowns as zero. An AVERAGENAN operator > for a CDEF would seem to complete the loop. > > Any suggested starting points for adding this to rrdtool? I haven't > dug through the source before. search for the name of the consolidation function in the source ... it is sort of orderly ... cheers tobi > > Cheers, > > Derek > > On Wed, Aug 22, 2012 at 2:50 AM, Tobias Oetiker <[email protected]> wrote: > > Hi Derek, > > > > Yesterday Derek Haynes wrote: > > > >> Several times on the list, the topic of a CF SUM function has > >> risen...just a sample: > >> > >> http://oss.oetiker.ch/rrdtool/forum.en.html#nabble-td1059458 > >> http://oss.oetiker.ch/rrdtool/forum.en.html#nabble-td1059458 > >> http://oss.oetiker.ch/rrdtool/forum.en.html#nabble-td1059458 > >> > >> I'm in need of a similar CF SUM function and I was curious if there > >> isn't one because (1) there's a fundemental reason why it's not > >> provided or (2) it just hasn't been implemented. > > > > the fundamental problem with a SUM CF is that the values of the RRA > > entries would then depend on the step interval of the RRA and thus > > fundamentally change the nature of the RRAs ... > > > >> For reason (1), the common argument is you can calculate this by > >> multiplying the average by the duration of the CDP. However, this > >> doesn't hold when a CDP contains unknowns as the average is only based > >> on the known values. > > > > basing a sum on unknown values might be problematic too > > > > a + unknown = a > > > > would mean that you assume that unknown equals 0 > > > > where we curently make the assumtion that the unknown part of the > > periode was similar to the known parts ... > > > > in any event, on a technical level, what would be required to > > achieve what you want (appart for the handling of unknown periodes > > within a single step) would be an AVERAGE_UNKNOWN_AS_ZERO > > consolidation function ... this would not break the assumptions > > about the nature of RRAs and you could calculate your type of SUM > > easily ... > > > > cheers > > tobi > > > > > >> The TOTAL operator does exactly what I'm looking for but it's only for > >> VDEF statements. > > > > > >> Any thoughts? > >> > >> Derek > >> > >> > > > > -- > > Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland > > http://it.oetiker.ch [email protected] ++41 62 775 9902 / sb: -9900 > > > > -- Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland http://it.oetiker.ch [email protected] ++41 62 775 9902 / sb: -9900 _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
