[rrd-users] Problems with multi-DS RRD that gets asynchronous-DS updates

steve rader rader at teak.wiscnet.net
Fri Sep 17 00:37:29 MEST 1999

My near-term graphs aren't looking too great.  This is caused
by the fact that my multi-DS RRDs get asynchronous-DS updates.
Here's a specific example that illustates the problem:

I have an "MRTG-like" rrd, straight from the rrdtutorial "A Real
World Example".

A collection script runs every 5 minutes.  It did:

  rrdtool update MadisonSD.rrd 937503600:475724299:104956107

Then at 1999-09-16 12:45:00 CDT, it did snmpgets across
a second boundary so my script stuffed values into rrd via:

  rrdtool update MadisonSD.rrd -t input 937503900:496053104
  rrdtool update MadisonSD.rrd -t output 937503901:108120595

I expect the value of the DS output at 1999-09-16 12:45:00 CDT to be
1.058e+04 = (108120595 - 104956107) / 300.

But instead I get NaN:

  <!-- 1999-09-16 12:45:00 CDT --> <row><v> 6.7762683333e+04 </v> \
    <v> NaN </v></row>

So about 1/10th of my data values are "NaN" and thus a
last-four-hour graph looks pretty bad because 1/10th of the
LINEs and AREAs are at zero. =:(

I'd like rrdtool to take the PDP for the DS output at 937503901 and
calculate a reasonable VALUE for the DS output at 937503900.

Comments?  Is this a bug?  Is this user error?  

- - -
systems guy

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