Two possibilities: caching. make sure to run each query several times in a row. zone reclaim mode. If this has gotten turned on turn it back off. How to tell: sysctl -n vm.zone_reclaim_mode Output should be 0. If it's not, then add this to /etc/sysctl.conf: vm.zone_reclaim_mode=0 and run: sudo sysctl -p and see if that helps.
pgsql-performance by date:
Соглашаюсь с условиями обработки персональных данных