RRD stats have many dropouts in all databases, with DHCPD RRD logging enabled and broken reverse DNS
Seen on pfSense 2.5.2 Community Edition:
Since about 2021/03/01 I've had a problem where my RRD data has dropouts (shortly after 2.5.0 release, hmm). It seems to have been completely dead from about 2021/05/02 (shortly after 2.5.1 release, hmm) to 2021/11/05. Looking at the RRD databases directly shows lots of empty records.
Digging around, I found that I had dhcpd RRD logging enabled, which causes the generated
updaterrd.sh to call
/usr/local/bin/dhcpd_gather_stats.php , which was taking a minute+ to run on my system. It does
gethostbyaddr() on each lease, and I did not have reverse DNS set up on the internal network, so
gethostbyaddr() was stalled by a maybe 5 second timeout each time. Setting up reverse DNS seems to have resolved the issue. I don't know exactly how the long delay caused RRD stats collection to break.
This appears to have been fixed in master (and RELENG_2_6_0! yay!) for a different problem in bug #11512. So I believe this bug is actually a duplicate of that with rather different symptoms, and I'm posting it to help others who might have similar symptoms.
Bug #12338 is another thing that might or might not be connected to this.