We are using Hibernate3.0 for mapping Oracle 8i DB, Our Application looks like a google search intranet application,
We need to store each and every search details in DB. Later to generate the Reports.

Now Our requirement Constraint is we should get the reports in less than 8secs. But Right Now if the records are around 500, we are getting in 8 secs,But if the records are around 2500 it is taking 17 secs. We thought to increase the performance of our application in Hibernate Side.

Our Production Environment:

Tomcat Server
Unix Box
J2EE application
Struts--we used tomcat dbcp connection pooling
Oracle DB.
Hibernate

What are the key areas we need to concentrate on increasing the performance.

You problem description is a bit vague so I cannot give the siver bullet answer ;-)

First thing to do is to make sure that the Hibernate layer is your bottleneck. You cannot optimize an application with statements like "I thought that..." You've got to find the bottleneck, optimize it, find the new bottleneck etc.

I would start with DB profiling, get the most time consuming queries. If they are fast but are issued too often, you might want to look at 2nd level cache, query optimisations, association level batchs... If they are slow, ask for the query plan and check that it uses the indexes as you expect.

If you're using cache, make sure that it's correctly sized. If cache entries are evicted as soon as they get in, the cache becomes a performance hit. If you're not using cache, use it !