Statistics on index usage

On Tue, Nov 1, 2016 at 8:43 AM, François Battail
<francois.battail@sipibox.fr> wrote:

Dear List,

does pgsql maintains statistics on index usage? I mean just a counter
for each index in the database, incremented each time time it is used.
It would be useful to help cleaning almost unused index and to avoid
poisoning the global cache.

I've found nothing so far but may be I've been missing something.

Yup it does keep track of index usage. To see all the various stuff
postgres keeps track of etc, try typing

select * from pg_ then hit tab. The two common ones I look at are:

pg_statio_all_indexes
pg_stat_user_indexes

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On Tue, Nov 1, 2016 at 10:43 AM, François Battail <
francois.battail@sipibox.fr> wrote:

Dear List,

does pgsql maintains statistics on index usage? I mean just a counter
for each index in the database, incremented each time time it is used.
It would be useful to help cleaning almost unused index and to avoid
poisoning the global cache.

I've found nothing so far but may be I've been missing something.

Best regards.

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does pgsql maintains statistics on index usage?

Yes, try this query. Look at idx_scna, & idx_tup_fetch

SELECT n.nspname as schema,
i.relname as table,
i.indexrelname as index,
i.idx_scan,
i.idx_tup_read,
i.idx_tup_fetch,
CASE WHEN idx.indisprimary
THEN 'pkey'
WHEN idx.indisunique
THEN 'uidx'
ELSE 'idx'
END AS type,
idx.indisexclusion,
pg_get_indexdef(idx.indexrelid),
CASE WHEN idx.indisvalid
THEN 'valid'
ELSE 'INVALID'
END as statusi,
pg_relation_size(quote_ident(n.nspname)|| '.' ||
quote_ident(i.relname)) as size_in_bytes,
pg_size_pretty(pg_relation_size(quote_ident(n.nspname)|| '.' ||
quote_ident(i.relname))) as size
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.relname LIKE '%%'
AND n.nspname NOT LIKE 'pg_%'
ORDER BY 1, 2, 3;

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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.