Hibernate second level cache questions

forumuser1080 · **Joined:** Mon Dec 21, 2009 3:43 pm **Posts:** 24

I am trying to find out if enabling the second level cache provided by hibernate will help my performance and after reading through the documentation I am still a little confused and i have a couple of questions.

1. Do entities get stored in the second level cache even when you are asking for an entity by something other than its primary key?

i.e.

Code:

    
public class Field implements Serializable {
   
   private long id;
   private String name;
   private String category;
.
.

I search for Field's by name or name and category based on different criteria. So I cannot make name and category a composite primary key because category can sometimes be null. Lets say I do the following multiple times

Code:

   
String query = "SELECT f FROM Field f WHERE f.name = :name and f.category = :category";
         
entityManager.createNamedQuery(query)
            .setParameter("name", name)
                .setParameter("category", category)
            .getSingleResult()

The name and category are the same for a lot of the queries, so I really do not want to go out to the db every time I perform this query. If I turn on the second level cache will I avoid going to the db every time I make this query?

Cameron McKenzie · **Posted:** Fri Jan 29, 2010 10:55 am

You will only hit the cache if you ask for an entity by its id.

Hibernate FAQ
Discussion

pb00067 · **Joined:** Tue Jun 16, 2009 3:36 am **Posts:** 990

Quote:

You will only hit the cache if you ask for an entity by its id.

This is not completely true. Because beyond

Code:

hibernate.cache.use_second_level_cache=true

you could also activate the second level query cache

Code:

hibernate.cache.use_query_cache=true

Activating the second level query cache allows you to cache also queries (together which its result set)
into 2L-cache.
Furthermore you must tell hibernate explicitely to put the query into 2L cache
mynamedQuery.setCacheable(true);
Also it is important to have the 2L itself enabled and regarding persistent class configured for being cached into 2Lcache.
Otherwise second level query cache is contraproductive.

pb00067 · **Joined:** Tue Jun 16, 2009 3:36 am **Posts:** 990

Quote:

1. Do entities get stored in the second level cache even when you are asking for an entity by something other than its primary key?

Yes. (provided that regarding entity class is configured for being cached into 2L Cache)