[rrd-developers] re fetching most recent DS values

steve rader rader at ginseng.hep.wisc.edu
Tue May 22 20:56:26 MEST 2001

If you update an RRD, let the next CDP time pass and then do
"rrdtool fetch some.rrd -s now" before the next update, you get
"NaN".  So "rrdtool fetch ... -s now" doesn't always report
the most "recent" DS values... for example...

 11:01  update causes DS to have the value 3 at 11:00
 11:02  "rrdtool fetch -s now" returns 3 for 11:00 
 11:06  "rrdtool fetch -s now" returns NaN for 11:05
 11:07  update causes DS to have the value 6 11:05

I've hacked "dsreport -now" to report values from the second
to the most current CDP when the last update is less than the
most current CDP time.

But I'm left wondering: can anyone think of a non-kludgy

I'd rather not have to duplicate this kludge in various
contexts, so I think there should be a native way to get
recent values from RRDtool... something like...

 rrdtool recent-values some.rrd AVERAGE

I'd do the work myself but last time I tried to add a new
flavor of rrdtool command, trying to get the perl bindings
working without documentation left me dazed and confused!

If anyone understands perl-shared/* and is willing to help me
get over a hump or two, please contact me off list.  Thanks.

Also, if anyone knows of a reference with details etc about
the C/perl bindings interface, please let me know.

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

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