oracle delete query taking too much time

Question

I have a query like

DELETE from tablename where colname = value;

which takes awfully long time to execute. What could be the reason? I have

Answer 1

So I'll just post my experience. Might be helpful for someone.

The query

delete from foo
where foo_id not in ( 
  select max(foo_id) from foo group by foo_bar_id, foo_qux_id
);

took 16 sec. deleting 1700 records from 2300 total in table foo.

I checked all the indexes on foreign keys as directed in other answers. That did not help.

Solution:

Changed the query to

delete from foo
where foo_id in ( 
  select foo_id from foo
  minus
  select max(foo_id) from foo group by foo_bar_id, foo_qux_id
);

I've changed not in to in and used minus to achieve correct result.

Now the query executes in 0.04 sec.