vacuum_cost_delay
No restart — settable per sessiontime (ms)
The pause manual VACUUM takes after hitting vacuum_cost_limit (default 0 = no throttle).
What it does
The companion sleep duration for the manual-VACUUM throttle. The default of 0 means manual VACUUM is not throttled at all — it finishes as quickly as the storage allows. autovacuum_vacuum_cost_delay is the separate, throttled counterpart for the autovacuum daemon.
How to tune it
Leave at 0 so manual VACUUMs finish promptly. If a manual VACUUM is visibly hurting foreground latency on slow storage, raise it briefly for that session. For autovacuum tuning, set autovacuum_vacuum_cost_delay.