How we halved DNS build delay and cut memory use by 85%

When I last wrote about our DNS propagation pipeline in 2022, the Zone Builder received about 250 DNS record changes per second. Today it receives about 700, nearly three times as many, plus about 100 other events, such as zone setting changes. However, the number of events was never the real problem. The problem was the kind of work some of those events needed, and how that work grows with the size of a zone. Some zones now hold more than 20 million records, and we expect them to keep growing toward hundreds of millions. Each event starts a clock that measures how long it takes us to turn that change into data our authoritative DNS servers can use. We call that work a build. A build reads the current database state, converts it into the format used at the edge, and writes any changes to Quicksilver. In 2022, per-record builds were 150 times faster than full builds on average. On a test zone with one million records, per-record builds were 4,250 times faster. We ended that post with the obvious next step: do the same thing for zone settings. Why doesn't the Zone Builder just rebuild the setting that…