[rrd-users] Understanding RRD's; Question #3

[Dave Bodenstab]

I'm trying to understand what's going on with rrdtool
so I've been creating a test rrd file and examining
the results.

My third question is about rrdfetch.  Here's what I did:

  $ rrdtool create test.rrd \
  		--start '12 am 1/1/2001' \
		--step 86400 \
		DS:one:ABSOLUTE:86400:U:U \
		RRA:LAST:0.5:1:5

  $ rrdtool dump test.rrd | fgrep '<row>'
  <!-- 2000-12-27 18:00:00 CST / 977961600 --> <row><v> NaN </v></row>
  <!-- 2000-12-28 18:00:00 CST / 978048000 --> <row><v> NaN </v></row>
  <!-- 2000-12-29 18:00:00 CST / 978134400 --> <row><v> NaN </v></row>
  <!-- 2000-12-30 18:00:00 CST / 978220800 --> <row><v> NaN </v></row>
  <!-- 2000-12-31 18:00:00 CST / 978307200 --> <row><v> NaN </v></row>

  $ n=1
  $ while [ $n -le 5 ]
  > do
  > t=$(( 978307200 + $n * 86400 ))
  > rrdtool update test.rrd $t:$RANDOM
  > n=$(( n + 1 ))
  > done

  $ rrdtool fetch test.rrd LAST -s '1/3/2001' -e '1/3/2001'
	one
   978566400: 2.8596064815e-01
   978652800: 1.4814814815e-01

  $ date -d '0:0:0 1/1/1970 utc + 978566400 sec'
  Wed Jan  3 18:00:00 CST 2001
  $ date -d '0:0:0 1/1/1970 utc + 978652800 sec'
  Thu Jan  4 18:00:00 CST 2001

So, why is rrdfetch giving me 1/4's data?  I only wanted one
day's value.  Is this a bug?  Maybe it's because the time slots
are not aligned on a day?  (Refer to my question #1)  


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