$ heroku pg:diagnose
RED: Hit Rate
Name Ratio
────────────────────── ──────────────────
overall index hit rate 0.9311722873276731
overall cache hit rate 0.6373249488053885
GREEN: Connection Count
GREEN: Long Queries
GREEN: Idle in Transaction
GREEN: Indexes
GREEN: Bloat
GREEN: Blocking Queries
GREEN: Sequences
SKIPPED: Load
この指標はVACUUMしても変化しないんだろうけど。