On 1/30/07, Simon Hobson <[EMAIL PROTECTED]> wrote:
Ben Griffith wrote: >Doesn't it just add up all the entries to get a total for the hour, >then from that a rate per second? Or does it actually compute the >rate throughout the hour, on the fly? No, it ALWAYS computes an average/max/min depending on what you set in the rrd. Also, you NEED to use average or your figures are guaranteed to be wrong. For example, suppose we just look at 4 samples : 1 1 0 0 Clearly your boiler was running for half the time (give or take a bit due to the sampling), and average would give you 0.5. Max would give you 1 for any period where the boiler ran at all which is not what you want.
The 1 1 0 0 are counter values, so they are added together and then divided by the step interval. In this case, if the interval was 4 minutes (240 seconds) that would mean 2/240. Since I've set up the RRA to contain only one step (size 1 hour), it's like Alex said: "MIN(x) = MAX(x) = AVG(x) = LAST(x) if there's only one x." If I had said the step size was 15 minutes and the RRA contained 4 of them then I'd be in trouble. I didn't know how all of that worked when I set it up, so I guess I just lucked out. I think I've got it now though. I agree that even though MAX works just fine in this case it is misleading.
>filename=/usr/local/misterhouse/trunk/data/rrd/Burner_Counter.rrd >timenow=`date | sed 's/:/\\\:/g'` >rrdtool graph /home/griffith/public_html/boiler_day.png \ > --end 00\:00 --start end-7d --x-grid >DAY:7:DAY:7:DAY:1:86400:%A \ > --height 200 --width 500 --imgformat PNG \ > --title "Boiler run-time per day" --vertical-label "minutes" \ > DEF:day1=$filename:minutes:MAX:start="midnight >yesterday - 6d":end=start+23h \ Two things wrong here (I think) : First, you don't want max, you want average (see above) Second, I think you need "start+24h" not "start+23h"
That's what I thought too, but "start+24h" and "start+1d" both gave me 25 hours of data instead of 24, and my "bars" overlapped from midnight to 1am. The totals are correct when I use +23h. I guess by saying start is "midnight yesterday" I get that first hour, and then I want 23 more hours, not 24. That doesn't seem right. Did I find a bug? I'm using 1.2.15-r3 from Gentoo portage. -Ben
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