Apache Cayenne Documentation - Performance Tuning

Most performance problems in database applications, including those using ORM, are related to the inefficient queries and/or large volumes of data in the database. Here is a few common issues that a typical application may run into:

Converting a large ResultSet into objects takes very long time.
Storing objects from a large ResultSet takes large amounts of memory. Application may eventually run out of memory and crash.
Given a list of objects, there may be a need to retrieve a list of related objects. Often this is done in a suboptimal way, by issuing a single query for each dependent object.

There is no single solution to all performance problems. Cayenne offers a few strategies to improve performance. They should be applied where appropriate.