autovacuum_vacuum_threshold

The fixed part of the vacuum trigger, default 50 rows. On any real table the scale factor dwarfs it, until you set the factor to 0, at which point the threshold alone decides the cadence: dead rows arrive at your write rate, and vacuum fires every threshold ÷ rate. That inversion is the core of cadence-first tuning, and it is why this obscure default matters more than it looks.