Root zone performance regression since 9.12.2rc2 and 9.13.1
Sometime around 26th June something has changed BIND's root zone performance for the worse (much worse in 9.12.2rc2).
9.13.1 https://perflab.isc.org/#/config/run/56b0925d6e2121101760eac6/
9.12.2rc2 https://perflab.isc.org/#/config/run/5a326d0249902c8a028b9ced/
The (much slower) 9.11.4rc1 release around the same time appears unaffected.