Are you saying that there is a discrepancy between what MIN and MAX report, vs. what can be seen on the graph?
If so: are you sure you use the same (C)DEF to get min and max from? > Hi Alex, > > Thanks for that, I'll study this some more. > > For now I'm doing it the "messy" way, i.e. fetch-ing all the data into an > array, sorting it numerically ascending and then taking the first and last > values of the array as minimum and maximum values plotted on the graph. > > As I say it's not as clean as using an rrdtool function directly to > extract > min/max, but it seems to give results which correlate exactly to the > minimum > and maximum points plotted on the graphs which is the main thing. > > Thanks, > Oliver. > > -----Original Message----- > From: Alex van den Bogaerdt > Sent: Thursday, August 11, 2011 11:05 PM > To: Oliver > Cc: [email protected] > Subject: Re: [rrd-users] VDEF MINIMUM > > bottom paragraph of my reply, "... the other ..." is the relevant part > then. You want to display a certain amount of RRA rows in less the amount > of pixel columns, so RRDtool is going to do some on the fly consolidation. > > Try an end time which is n*60, try to display 400*60 seconds, do so in 400 > pixel columns. > GPRINT last, min, average, max. > Now try the same, except that you display 400*30 seconds. > > This part of the tool has had more than its fair share of problems in the > past, I seem to recall an off by one error or two, and other problems. > There could be differences between the various RRDtool versions, but all > versions will have some form of on the fly consolidation, where multiple > RRA rows will be combined into one pixel row. > > Once you understand the relatively easy n*30 vs. n*60 case, try to figure > out what the tool does with n*40, n*50 and so on. > > GPRINTing the time component of the first and last sample on the graph may > also be interesting. > > cheers, > Alex > > >> Hi Alex, >> >> Thank you for your detailed reply which has certainly helped me >> understand >> RRA calculations a bit better. >> >> However I am only using one RRA (I should have pointed this out in my >> first >> post): >> >> filename = "noise.rrd" >> rrd_version = "0003" >> step = 30 >> last_update = 1313098265 >> ds[noise].type = "GAUGE" >> ds[noise].minimal_heartbeat = 60 >> ds[noise].min = NaN >> ds[noise].max = NaN >> ds[noise].last_ds = "9.4" >> ds[noise].value = 5.6364270600e+01 >> ds[noise].unknown_sec = 0 >> rra[0].cf = "AVERAGE" >> rra[0].rows = 5760 >> rra[0].cur_row = 4995 >> rra[0].pdp_per_row = 1 >> rra[0].xff = 5.0000000000e-01 >> rra[0].cdp_prep[0].value = NaN >> rra[0].cdp_prep[0].unknown_datapoints = 0 >> >> Does this influence your previous reply? >> >> Thanks, >> Oliver. >> >> -----Original Message----- >> From: Alex van den Bogaerdt >> Sent: Tuesday, August 09, 2011 2:00 PM >> To: [email protected] >> Subject: Re: [rrd-users] VDEF MINIMUM >> >> You are looking at averages. Your two tests use different RRAs. For >> instance: one RRA consolidates 1 PDP into 1 CDP, the other consolidates >> 3 >> PDPs into one CDP. Look at 10,20,30,40,50,60. One RRA has all 6 values, >> the other RRA has average(10,20,30) equals 20, average(40,50,60) equals >> 50. >> >> minimum(10,20,30,40,50,60) equals 10. minimum(20,50) equals 20. Your >> test >> would return 10 and 20. >> >> It should work much better if you look at minimums of minimums: >> >> The other RRA would contain min(10,20,30) equals 10, min(40,50,60) >> equals >> 40. Then min(10,20,30,40,50,60) and min(10,40) both return 10. >> >> There can be two places where consolidation takes place. One is when >> data >> is copied into RRAs, the other is when rrdtool graph needs data in a >> resolution which is not available. If you take both into account, you >> should be able to get predictable results. >> >> HTH >> Alex >> >> _______________________________________________ >> rrd-users mailing list >> [email protected] >> https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users >> >> > > > _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
