How to identify un-used indexes in PostgreSQL
Josh Berkus’s excellent blog has the answer:
SELECT idstat.relname AS table_name,
indexrelname AS index_name,
idstat.idx_scan AS times_used,
pg_size_pretty(pg_relation_size(idstat.relname)) AS table_size, pg_size_pretty(pg_relation_size(indexrelname)) AS index_size,
n_tup_upd + n_tup_ins + n_tup_del as num_writes,
indexdef AS definition
FROM pg_stat_user_indexes AS idstat JOIN pg_indexes ON indexrelname = indexname
JOIN pg_stat_user_tables AS tabstat ON idstat.relname = tabstat.relname
WHERE idstat.idx_scan < 200
AND indexdef !~* 'unique'
ORDER BY idstat.relname, indexrelname;