Re: Queries for unused/useless indexes

On 2015-05-22 09:41:57 -0400, Melvin Davidson wrote:
> I'd like to share those queries with the community, as I know there must be
> others out there with the same problem.
>
> /* useless_indexes.sql */
> SELECT
>        idstat.schemaname AS schema,
>        idstat.relname AS table_name,
>        indexrelname AS index_name,
>        idstat.idx_scan AS times_used,
>        pg_size_pretty(pg_relation_size(quote_ident(idstat.schemaname) || '.' ||
> quote_ident(idstat.relname))) AS table_size,
>        pg_size_pretty(pg_relation_size(quote_ident(idstat.schemaname) || '.' ||
> quote_ident(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.schemaname,
>          idstat.relname,
>          indexrelname;

Thanks, that's useful.

However, it doesn't quite work if there are indexes with the same name
in different schemas. Better join on the schemaname, too:

    FROM pg_stat_user_indexes AS idstat
    JOIN pg_indexes AS idx ON indexrelname = indexname and idstat.schemaname = idx.schemaname
    JOIN pg_stat_user_tables AS tabstat ON idstat.relname = tabstat.relname and idstat.schemaname = tabstat.schemaname

(for some reason that makes it a lot slower, though)

    hp

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