PG cache hit ratio

gistfile1.sql

-- https://devcenter.heroku.com/articles/cache-size

-- Cache hit ratio for PG Tables
SELECT 
  sum(heap_blks_read) as heap_read,
  sum(heap_blks_hit)  as heap_hit,
  (sum(heap_blks_hit) - sum(heap_blks_read)) / sum(heap_blks_hit) as ratio
FROM 
  pg_statio_user_tables;

-- Indexes
SELECT 
  sum(idx_blks_read) as idx_read,
  sum(idx_blks_hit)  as idx_hit,
  (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as ratio
FROM 
  pg_statio_user_indexes;