.tip

The default triggers a vacuum when 20 percent of a table changed. On a 100 million row table that is 20 million dead rows before anything happens, and the table doubles in size in between.

ALTER TABLE events SET (
  autovacuum_vacuum_scale_factor = 0.01,
  autovacuum_vacuum_cost_delay = 2
);

One percent on the hot tables, defaults everywhere else. Watch n_dead_tup in pg_stat_user_tables to find the tables that need it.