[collectd] Postfix Delay graph NaN

[Chris Dombroski]

I have the tail plugin configured to follow the postfix log as detailed on
the wiki[1]. However, it seems that a combination of using the gauge type
along with not enough traffic causes the graph to show NaN at any interval
greater than a couple of hours[2][3] (the counter based data sources seem
to work correctly[4]). What can/should I do to get this graph working
correctly?

[1]: http://collectd.org/wiki/index.php/Plugin:Tail/Config
[2]:
http://collectd.icanttype.org/cgi-bin/drraw/drraw.cgi?Template=1291062473.8601&Base=/var/lib/collectd/rrd//aether.icanttype.org/tail-postfix/gauge-delay.rrd&Mode=view
[3]:
http://collectd.icanttype.org/cgi-bin/drraw/drraw.cgi?View=-1&Template=1291062473.8601&Base=/var/lib/collectd/rrd//aether.icanttype.org/tail-postfix/gauge-delay.rrd&Start=12/1/2010+06:30&End=12/1/2010+8:30&Mode=view&Shift=&Count=
[4]:
http://collectd.icanttype.org/cgi-bin/drraw/drraw.cgi?Mode=view&Template=1291066343.8890&Base=/var/lib/collectd/rrd//aether.icanttype.org/tail-postfix/counter-connection-in-TLS-established.rrd