[rrd-users] Two archives, one clobbered?

Mike Schilli b2b at perlmeister.com
Sun Mar 28 11:23:41 MEST 2004

Hey guys,

looks like I haven't fully understood how round robin databases are
working (although I thought I had :).

Here's what I'm trying to do:

      rrdtool create /tmp/mydemo.rrd --step=60  \
        --start=1080460430 DS:load:GAUGE:90:U:U \
        RRA:MAX:0.5:1:5 RRA:MAX:0.5:5:10

I'm creating two archives, one storing 5 single sample values, and
another one, storing 10 times the MAX of 5 samples. Adding data:

      rrdtool update /tmp/mydemo.rrd 1080460440:1000
      rrdtool update /tmp/mydemo.rrd 1080460500:1100
      rrdtool update /tmp/mydemo.rrd 1080460560:1200
      rrdtool update /tmp/mydemo.rrd 1080460620:1300
      rrdtool update /tmp/mydemo.rrd 1080460680:1400
      rrdtool update /tmp/mydemo.rrd 1080460740:1500
      # rrdtool update /tmp/mydemo.rrd 1080460800:1600

      rrdtool fetch /tmp/mydemo.rrd MAX \
          --start=1080460430 --end=1080460800

This prints what I would expect (although I'm puzzled why the first item
is missing):

      1080460380: nan
      1080460440: nan
      1080460500: 1.1000000000e+03
      1080460560: 1.2000000000e+03
      1080460620: 1.3000000000e+03
      1080460680: 1.4000000000e+03
      1080460740: 1.5000000000e+03
      1080460800: nan

But if I uncomment the line

      # rrdtool update /tmp/mydemo.rrd 1080460800:1600

in the script above, I  get

      1080460200: nan
      1080460500: nan
      1080460800: 1.6000000000e+03

I thought I'd get the values of the first archive (for the last 5*60
secs) plus the MAX of 5 values for the second archive. But it seems like
it clobbers the first archive. Any ideas what I'm doing wrong? Any help

-- Mike
Mike Schilli
m at perlmeister.com

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