Pdns - cache-ttl

cache-ttl - это время жизни одинаковых запросов в кэше, для того чтобы повторно не обрщаться к pdns серверу.
По-умолчанию, 20 секунд.

# vi /etc/pdns/pdns.conf
cache-ttl=300
# systemctl restart pdns

PowerDNS by default uses the ‘Packet Cache’ to recognise identical questions and supply them with identical answers, without any further processing. The default time to live is 20 seconds and can be changed by setting cache-ttl. It has been observed that the utility of the packet cache increases with the load on your nameserver.
Not all backends may benefit from the packet cache. If your backend is memory based and does not lead to context switches, the packet cache may actually hurt performance.