Re: Queries for unused/useless indexes

[Melvin Davidson <melvin6925@xxxxxxxxx>]

I'm not sure why you are using "pg_stat_user_indexes". My original query below uses "pg_stat_all_indexes" and the schema names are joined and it does work.


SELECT n.nspname as schema,
       i.relname as table,
       i.indexrelname as index,
       i.idx_scan,
       i.idx_tup_read,
       i.idx_tup_fetch,
       pg_size_pretty(pg_relation_size(quote_ident(n.nspname) || '.' || quote_ident(i.relname))) AS table_size,
       pg_size_pretty(pg_relation_size(quote_ident(n.nspname) || '.' || quote_ident(i.indexrelname))) AS index_size,
       pg_get_indexdef(idx.indexrelid) as idx_definition
  FROM pg_stat_all_indexes i
  JOIN pg_class c ON (c.oid = i.relid)
  JOIN pg_namespace n ON (n.oid = c.relnamespace)
  JOIN pg_index idx ON (idx.indexrelid =  i.indexrelid )
 WHERE i.idx_scan < 200
   AND NOT idx.indisprimary
   AND NOT idx.indisunique
 ORDER BY 1, 2, 3;

On Mon, May 25, 2015 at 10:41 AM, Peter J. Holzer <hjp-pgsql@xxxxxx> wrote:

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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--

Melvin Davidson
I reserve the right to fantasize.  Whether or not you
wish to share my fantasy is entirely up to you.