Unused Indexes - PostgreSQL Database

Question

I have used attached query to check unused indexes in my EDB9.5 DB. It's showing attached indexes are the unused indexes. Is it safe to drop below unused indexes?

SELECT
    idstat.relname AS TABLE_NAME,
    indexrelname AS index_name,
    idstat.idx_scan AS index_scans_count,
    pg_size_pretty(pg_relation_size(indexrelid)) AS index_size,
    tabstat.idx_scan AS table_reads_index_count,
    tabstat.seq_scan AS table_reads_seq_count,
    tabstat.seq_scan + tabstat.idx_scan AS table_reads_count,
    n_tup_upd + n_tup_ins + n_tup_del AS table_writes_count,
    pg_size_pretty(pg_relation_size(idstat.relid)) AS table_size
FROM
    pg_stat_user_indexes AS idstat
JOIN
    pg_indexes
    ON
    indexrelname = indexname
    AND
    idstat.schemaname = pg_indexes.schemaname
JOIN
    pg_stat_user_tables AS tabstat
    ON
    idstat.relid = tabstat.relid
WHERE
    indexdef !~* 'unique'
    and idstat.relname='cwt_act'
ORDER BY
    idstat.idx_scan DESC,
    pg_relation_size(indexrelid) DESC;

Please suggest!

Answer 1

You are missing a few points:

• there could be a GiST index supporting an exclusion constraint

• an index on an expression can help the optimizer get better estimates for that expression, even if it isn't scanned

I recommend the query from my blog:

SELECT s.schemaname,
       s.relname AS tablename,
       s.indexrelname AS indexname,
       pg_relation_size(s.indexrelid) AS index_size
FROM pg_catalog.pg_stat_user_indexes s
   JOIN pg_catalog.pg_index i ON s.indexrelid = i.indexrelid
WHERE s.idx_scan = 0      -- has never been scanned
  AND 0 <>ALL (i.indkey)  -- no index column is an expression
  AND NOT i.indisunique   -- is not a UNIQUE index
  AND NOT EXISTS          -- does not enforce a constraint
         (SELECT 1 FROM pg_catalog.pg_constraint c
          WHERE c.conindid = s.indexrelid)
ORDER BY pg_relation_size(s.indexrelid) DESC;