/* Total size of all the indexes on each table, descending by size */
SELECT
c.relname AS table, pg_size_pretty(pg_indexes_size(c.oid)) AS index_size
FROM
pg_class c
LEFT JOIN
pg_namespace n ON (n.oid = c.relnamespace)
WHERE
n.nspname NOT IN ('pg_catalog', 'information_schema') AND n.nspname !~ '^pg_toast' AND c.relkind='r'
ORDER BY
pg_indexes_size(c.oid) DESC;