SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
    AND C.relkind <> 'i'
    AND nspname !~ '^pg_toast'
  ORDER BY pg_total_relation_size(C.oid) DESC
  LIMIT 5;

输出如下:

      relation       | total_size 
----------------------+------------
 public.snapshots     | 823 MB
 public.invoice_items | 344 MB
 public.messages      | 267 MB
 public.topics        | 40 MB
 public.invoices      | 35 MB
(5 rows)