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. Cheers, Derek On Wed, Aug 22, 2012 at 2:50 AM, Tobias Oetiker <t...@oetiker.ch> 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 t...@oetiker.ch ++41 62 775 9902 / sb: -9900 -- Derek Haynes Scout Web Monitoring and Reporting ~ http://scoutapp.com Blog ~ http://blog.scoutapp.com 415.871.7979 _______________________________________________ rrd-users mailing list rrd-users@lists.oetiker.ch https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
