Re: Queries for unused/useless indexes

Melvin - thanks for sharing.

Here is the query I use which lists the percent of queries against the
table which use the index ordered by least used first.

The 'pg_relation_size(relid)>(5*8192)' is used to remove any tables that
would be so small the optimizer would just choose a table scan.

SELECT schemaname,
relname,
idx_scan,
seq_scan,
(100 * idx_scan / (seq_scan + idx_scan)) AS perc_idx_used
FROM pg_stat_user_tables
WHERE pg_relation_size(relid)>(5*8192)
AND NOT ((idx_scan=0
OR idx_scan=NULL)
AND seq_scan=0)
ORDER BY perc_idx_used;

*Will J. Dunn*
*willjdunn.com <http://willjdunn.com>*

On Mon, May 25, 2015 at 12:39 PM, Peter J. Holzer <hjp(at)hjp(dot)at> wrote:

> On 2015-05-25 12:25:01 -0400, Melvin Davidson wrote:
> > I'm not sure why you are using "pg_stat_user_indexes".
>
> Because you did. I didn't change that.
>
> > My original query below
> > uses "pg_stat_all_indexes" and the schema names are joined and it does
> work.
>
> I'm not sure what you mean by "original", but this:
>
> > 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;
>
> is not the query you posted in your original message.
>
> Here is what you posted:
>
> > On Mon, May 25, 2015 at 10:41 AM, Peter J. Holzer <hjp-pgsql(at)hjp(dot)at>
> 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;
>
> --
> _ | Peter J. Holzer | I want to forget all about both belts and
> |_|_) | | suspenders; instead, I want to buy pants
> | | | hjp(at)hjp(dot)at | that actually fit.
> __/ | http://www.hjp.at/ | -- http://noncombatant.org/
>