Re: Queries for unused/useless indexes

The query I previously sent was table level. Here is an index level one:
SELECT pg_stat_user_indexes.schemaname,
pg_stat_user_indexes.relname,
pg_stat_user_indexes.indexrelid,
pg_stat_user_indexes.indexrelname,
pg_stat_user_indexes.idx_scan,
pg_stat_user_tables.seq_scan,
(100 * pg_stat_user_indexes.idx_scan / (pg_stat_user_tables.seq_scan
+ pg_stat_user_indexes.idx_scan)) AS perc_idx_used
FROM pg_stat_user_indexes INNER JOIN pg_stat_user_tables ON
pg_stat_user_indexes.relid = pg_stat_user_tables.relid
WHERE pg_relation_size(pg_stat_user_indexes.relid)>(5*8192)
AND NOT ((pg_stat_user_indexes.idx_scan=0
OR pg_stat_user_indexes.idx_scan=NULL)
AND pg_stat_user_tables.seq_scan=0)
ORDER BY perc_idx_used;

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

On Tue, May 26, 2015 at 10:31 AM, William Dunn <dunnwjr(at)gmail(dot)com> wrote:

> 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/
>>
>
>