[knot-resolver-users] Why are some names not cached?

Hello, I am trying to figure out why some domain names are not resolving on my instance of Knot resolver over DoH with some clients. I was able to reproduce this issue with [doh](https://github.com/curl/doh) client built on libcurl. The problem never manifests with kdig (neither with DoH, nor DoT nor Do53). During this, I noticed something strange. For domain name github.com (which sometimes returns no A record), I always receive an answer with TTL set to 60. It seems like this name does not get cached at all. See the test output below. Interestingly, if I delete cache files and restart the resolver, the TTL starts decreasing as expected. Is this a sign that something was wrong with the cache before? Or is this some sort of cache optimization for low TTL records? Here is the test output: $ for i in `seq 1 5`; do ./doh github.com https://nscache.mtg.ripe.net/dns-query ; echo "----"; kdig +https +noadflag +nocookie +noall +answer github.com A @nscache.mtg.ripe.net ; echo "===="; sleep 1; done [github.com] TTL: 60 seconds AAAA: 0064:ff9b:0000:0000:0000:0000:8c52:7903 ---- github.com. 60 IN A 140.82.121.3 ==== [github.com] TTL: 60 seconds A: 140.82.121.3 AAAA: 0064:ff9b:0000:0000:0000:0000:8c52:7904 ---- github.com. 60 IN A 140.82.121.4 ==== [github.com] TTL: 60 seconds A: 140.82.121.4 AAAA: 0064:ff9b:0000:0000:0000:0000:8c52:7904 ---- github.com. 60 IN A 140.82.121.4 ==== [github.com] TTL: 60 seconds A: 140.82.121.4 AAAA: 0064:ff9b:0000:0000:0000:0000:8c52:7903 ---- github.com. 60 IN A 140.82.121.4 ==== [github.com] TTL: 60 seconds A: 140.82.121.3 AAAA: 0064:ff9b:0000:0000:0000:0000:8c52:7904 ---- github.com. 60 IN A 140.82.121.3 ==== -- Best regards, Ondřej Caletka