Re: Queries for unused/useless indexes

Will,

Much thanks. Let's keep up the sharing with the community.

On Tue, May 26, 2015 at 11:32 AM, William Dunn <dunnwjr(at)gmail(dot)com> wrote:

> 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/
>>>
>>
>>
>

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