[rrd-developers] Re: (bug?) Incorrectly selecting low-res RRA

Phil Radden P.Radden at rl.ac.uk
Fri Mar 28 17:49:14 MET 2003

On Thu, 27 Mar 2003, Alex van den Bogaerdt wrote:
> [very helpful explanation]

Hi Alex,

Thanks very much for your mail yesterday; I believe I now understand what 
you're suggesting (sorry for being slow!), so I've added some additional 
test to my monitoring script to try some extra things.

Unfortunately this debugging is going very slowly because I have to wait 
until the strange behaviour hits each time...

Based on other suggestions, I'd previously tried shifting back a time 
period equivalent to one row, to avoid what you described as the
'yet-to-be-archived-partially-filled-timeslot' (but not rounding to a 
multiple of that time period, as I now understand you to be suggesting)
but this made the situation worse, in that the lower resolution RRA was 
chosen for about twice as long last night.

This caused me to realise that the 'coverage before resolution' rule is 
also applying at the beginning of time, not just the end of time, and that 
my 'month' rra is only specified to include just the right amount of data 
- if I understand things better now!  That's probably a ganglia bug if 
anything, and I'll let them know.

In the meantime, tonight I'll be testing a variety of counts including

LINES=`rrdtool fetch "$CHECK" AVERAGE -s -2419200 -e N | wc -l`
LINES2=`rrdtool fetch "$CHECK" AVERAGE -s -2429280 -e -10080 | wc -l`
NOW=`date +%s`
LINES4=`rrdtool fetch "$CHECK" AVERAGE -s end-2419200 -e $RNDNOW1 | wc -l`
LINES5=`rrdtool fetch "$CHECK" AVERAGE -s -2419200 -e $RNDNOW1 | wc -l`
LINES6=`rrdtool fetch "$CHECK" AVERAGE -s end-2419200 -e $RNDNOW2 | wc -l`
LINES7=`rrdtool fetch "$CHECK" AVERAGE -s -2419200 -e $RNDNOW2 | wc -l`

to see if I really understand.

Thanks once again,

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