Which SQL command creates ExclusiveLock?

Hi everyone!

I have a web application that uses Postgresql on backend. The application performs selects, updates, inserts, and deletes by using Hibernate. Tables
contain indexed fields. When I run the following query, SELECT * FROM pg_locks, it shows that some transactions place
ExclusiveLock:

relation | database | transaction | pid | mode | granted
----------+----------+-------------+-------+-----------------+---------
16757 | 16976 | | 22770 | AccessShareLock | t
| | 17965163 | 22770 | ExclusiveLock | t

According to postgres documentation, all update operations place ROW EXCLUSIVE MODE locks, and
EXCLUSIVE MODE is not automatically acquired by any postgres SQL command. So, which command places
ExclusiveLock??? I suspect that indexes can account for this behaviour, but couldn't find anything in the docs.
I am also wondering why there is nothing shown in "relation" column. I think it is supposed to display a table or index id or any other
object that is being locked.

Thanks for help!

Dennis