[rrd-users] Re: Cricket/RRD fetch resolution problem (2nd try)

[Alex van den Bogaerdt]

Scott C. Kennedy wrote:

> And when I do a query for "-s "now-1month" I should pull 8930 values from the
> "5minUse" RRA, but sometimes I pull 374 values which seem to come from the
> "2hrAve" RRA instead of the  "5minUse" RRA. Now, I have some RRDs no longer
> being updated, due to the switch not being used anymore, and the data is
> historical, but still valid, and the problem doesn't seem to be related to the
> last updated field.

These kinds of problems are, indeed, not related to the last update
field.

8928 values of 5 minutes each is 31 days.  372 values of 2 hours each
is also 31 days.  RRDtool will return one more row (not two) namely
the value defining your start time.  This value is for an interval you
didn't really specify (as it defines starttime-5m to starttime).
If another extra row is returned, it will be the interval containing
your end time (as in: now == 22:37 so return interval 22:35 to 22:40).

Instead of specifying "-s now-1month" try to do these:
  -e 996782400 -s end-31days
  -e 996782700 -s end-31days
  -e 996784200 -s end-31days
  -e 996786000 -s end-31days
  -e 996786300 -s end-31days

It has to do with data availability.  If "now" is not an exact multiple
of 2 hours (in UTC time), you are querying for something that is not
available in the 2-hour RRA.  The closest match is the data in the
5-minute RRA.  Sometimes "now" happens to be n*7200 seconds since the
epoch and as it turns out the 2-hour RRA is choosen. 

If I'm right (I didn't test it, it's easy enough for you as you have the
database ready) then the first one will pull data from the 2-hour RRA
and the others will pull data from other RRAs (such as the 5-minute one).

Oh, and if everything is working as it should you can use the resolution
flag to rrdtool fetch.   *If* the time is an exact multiple of 2 hours,
you can choose which RRA to use.  However, if you try to select the
2-hour RRA but fail to query correct start and end times, it fails:
"--start 00:00 --end 22:00" will work (assuming a timezone that is an
even number of hours away from UTC) but "--start 00:05 --end 22:05" will
not work.  It will return data from the 5-minute RRA.

HTH
-- 
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