Hi,
I use Hibernate with JBoss Cache.

I have entities like below, All i want is to retrieve Last 20 messages posted by User's Friends.

UserEntity (Long id)
FriendEntity (Long id, User user, Friend friend)
MessageEntity(Long id, User owner, String message, Timestamp created);

Because of performance issues, i use NativeQuery with UNION, not IN.
For a User who have 1000 friends, i generate a query like:

(select * from messages where owner = 1 order by created DESC LIMIT 20)
UNION ALL
(select * from messages where owner = 2 order by created DESC LIMIT 20)
UNION ALL
(select * from messages where owner = 3 order by created DESC LIMIT 20)
...
997 more
...
ORDER BY CREATED DESC LIMIT 20

It gives me the result i want but it is the worst way i have ever used. How can i use cache in order to improve the performance of such a Query?

Thanks.