Note

Other useful size queries include pg_column_size() and pg_database_size().

A quick example of how to query this information across all the tables in the current database is as follows:

SELECT 
  nspname,
  relname,
  pg_size_pretty(pg_relation_size(C.oid)) AS "size"
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE nspname NOT IN ('pg_catalog', 'information_schema')
ORDER BY pg_relation_size(C.oid) DESC
LIMIT 20;

On a pgbench database with a lot of work done on it, and thus a large history table, output from this might look like the following:

 nspname  |        relname        |  size    
----------+-----------------------+--------
 public   | pgbench_accounts      | 13 MB
 public   | pgbench_history       | 12 MB
 public   | pgbench_accounts_pkey | 1768 kB
 public   | pgbench_branches      | 224 kB
 pg_toast | pg_toast_2618         | 208 kB
 public   | pgbench_tellers       | 32 kB

This shows the main issue with this simple...