[rrd-developers] confusion about the CF LAST

[steve rader]

Would someone please explain the CF LAST and it's purpose?!!
I can't find a discussion of what it should really do.

I think it would be nice if the CF LAST returned values from the last
data update but the enclosed script indicates otherwise.  The script
updates the DS ds1 with the value 10 way back in time but then using
the CF LAST actually returns the "now/current" value:

 logging value 10 at Mon Jan 10 09:56:06 2000 CST (947519766)
 last update was at Mon Jan 10 09:56:06 2000 CST (947519766)
 last value logged is 10.00 
 "last" as per CF LAST is NaN 

What gives?

steve
- - - 
systems & network guy
high energy physics
university of wisconsin
- - - 

#!/bin/bash

rrdtool create -b 947519465 last-confusion-test.rrd \
  DS:ds1:GAUGE:1800:0:U \
  RRA:AVERAGE:0.5:1:5
rrdtool update last-confusion-test.rrd -t ds1 947519466:10
echo "logging value 10 at Mon Jan 10 09:56:06 2000 CST (947519766)"
rrdtool update last-confusion-test.rrd -t ds1 947519766:10

cat <<_EOT_>./last-confusion-test.rrdcgi
#!/usr/local/nrg/bin/rrdcgi
last update was at <RRD::TIME::LAST last-confusion-test.rrd "%c %Z"> (<RRD::TIME::LAST last-confusion-test.rrd "%s">)
<RRD::GRAPH /dev/null --imginfo ''
  --end <RRD::TIME::LAST last-confusion-test.rrd "%s">
  DEF:ds1=last-confusion-test.rrd:ds1:AVERAGE
  PRINT:ds1:AVERAGE:"%.2lf"
>
last value logged is <RRD::PRINT 0>
<RRD::GRAPH /dev/null --imginfo ''
  DEF:ds1=last-confusion-test.rrd:ds1:AVERAGE
  PRINT:ds1:LAST:"%lf"
>
"last" as per CF LAST is <RRD::PRINT 0>
_EOT_
chmod 755 ./last-confusion-test.rrdcgi
./last-confusion-test.rrdcgi < /dev/null | grep last
rm -f ./last-confusion-test.rrdcgi


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