Tobi, would this syntax work for you for specifying the smoothing window? RRA:SEASONAL:seasonal period:gamma[:smoothing window]:rra-num
RRA:DEVSEASONAL:seasonal period:gamma[:smoothing window]:rra-num ...where smoothing window is a fraction of the period, between 0 (no smoothing) and 1 (a full season)? Evan Tobias Oetiker wrote: > Today Evan Miller wrote: > >> The Holt-Winters prediction code runs a data smoother periodically so that >> the >> first few periods of predictions look nice and clean. There are a number of >> flaws in the smoother, and I'd like to discuss what to do about them. >> >> 1. The time the smoother runs during the period is calculated by hashing the >> filename. Look: >> >> rrd_create.c line 586: current_rra->par[RRA_seasonal_smooth_idx].u_cnt = >> hashed_name % period; >> >> If you ask me, this is completely nonsensical. It means that if you create >> two >> identical archives and feed them identical data, they rarely produce >> identical >> predictions. This makes regression testing frustrating until you learn the >> big >> "secret" of naming your archives the same thing. > > Evan, just guessing (jake should know) ... the smoother produces > extra load and therefore it should not run on all rrds at the same > time ... can you judge what that load is ? > >> 2. The smoother runs at different times based on whether RRDtool has received >> individual updates or a bulk update with identical data. From a comment in >> rrd_update.c: >> >> /* calling the smoothing code here guarantees at most one smoothing >> * operation per rrd_update call. Unfortunately, it is possible with bulk >> * updates, or a long-delayed update for smoothing to occur off-schedule. >> * This really isn't critical except during the burn-in cycles. */ >> >> This behavior is counter-intuitive and complicates testing. > > yep > >> 3. The smoother takes a running average over 5% of a season. This 5% figure >> is >> hard-coded, and has produced quite awful predictions when I've set the season >> to be a week, since each point becomes an average over about 8 hours. >> >> I'm not sure about what to do about #2, but I think #1 should be made more >> consistent (say, run at a fixed interval), and #3 should perhaps be an input >> parameter, although I don't know the right interface for it. >> >> At IMVU, we've disabled the smoother altogether because of its problems. I >> wouldn't be averse to ripping out the smoother altogether, but I imagine >> others >> find the feature useful. > > this wold mean an extra parameter at RRA setup time ... > > unfortunately I have not used HW in production, so this is all a > guessing game to me ... > > cheers > tobi > _______________________________________________ rrd-developers mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-developers
