How to delete all index tables from postgres database? - postgresql

Question

I have quite a few index tables in my DB. I want to delete them and only index those tables that are very big. How Can i delete them?
I can do
select relname from pg_class where relkind='i'; and drop index
But I think this query will also delete some system tables. How do i do this without affecting thr functioning of the DB?

Answer 1

If you are using pg_class to find all indexes, you need to join that to pg_namespace and filter on the schema where your tables (and indexes) are stored.
It is much easier to pg_indexes instead though:
select schemaname,
indexname,
tablename,
format('drop index %I.%I;', schemaname, indexname) as drop_statement
from pg_indexes
where schemaname not in ('pg_catalog', 'pg_toast');
That will however also show you indexes that are used for primary keys.
If you want to exclude primary key indexes, you can use something like this:
select s.nspname as schemaname,
i.relname as indexname,
t.relname as tablename,
format('drop index %I.%I;', s.nspname, i.relname) as drop_statement
from pg_index idx
join pg_class i on i.oid = idx.indexrelid
join pg_class t on t.oid = idx.indrelid
join pg_namespace s on i.relnamespace = s.oid
where s.nspname not in ('pg_catalog', 'pg_toast')
and not idx.indisprimary;
If you also want to exclude unique indexes, just add and not idx.indisunique to the where condition.

Answer 2

Here a sample that actually drops the indices. Based on #a_horse_with_no_name answer.
DO $$
DECLARE
ind record;
BEGIN
FOR ind IN
SELECT
s.nspname as schemaname,
i.relname as indexname,
t.relname as tablename,
format('drop index %I.%I;', s.nspname, i.relname) as drop_statement
FROM pg_index idx
join pg_class i on i.oid = idx.indexrelid
join pg_class t on t.oid = idx.indrelid
join pg_namespace s on i.relnamespace = s.oid
WHERE s.nspname not in ('pg_catalog', 'pg_toast')
AND NOT idx.indisprimary
LOOP
RAISE NOTICE 'Command: %', ind.drop_statement;
EXECUTE ind.drop_statement;
END LOOP;
COMMIT;
END$$;