Does HQL update clear 2nd level cache?

Question

Native queries are clearing the 2nd level cache entries. An answer from the hibernate forum that is 7 years old says that HQL update queries also clear the 2nd level cache.

Answer 1

Native queries are clearing the 2nd level cache entries.

1. Native queries (actually this is only for native inserts/deletes/updates, not queries) are invalidating the 2nd level cache entries for all caches (WHOLE CACHE). I have verified this with the current stable version of Hibernate: 4.1.9. This is sensible because Hiberante can't possibly know what was changed in the DB, so the only option is to invalidate whole 2nd level cache. This can be a serious issue in some systems which relies heavily on the 2nd level cache.

There is though a possibility to specify what from 2nd level cache should be invalidated (or even specify that nothing is evicted from cache). Look at great blog post http://www.link-intersystems.com/bin/view/Blog/Hibernate%27s+second+level+cache+and+native+queries where this is explained thoroughly.

To prevent Hibernate from invalidating anything from cache:

SQLQuery sqlQuery = session.createSQLQuery("ALTER SESSION SET NLS_COMP = 'BINARY'");
sqlQuery.addSynchronizedQuerySpace("");  
int updatedEntities = sqlQuery.executeUpdate();

To instruct Hibernate to invalidate only the Person entity cache:

SQLQuery sqlQuery = session.createSQLQuery("UPDATE PERSON SET ... WHERE ...");
sqlQuery.addSynchronizedEntityClass(Person.class);
int updatedEntities = sqlQuery.executeUpdate();

An answer from the hibernate forum that is 7 years old says that HQL update queries also clear the 2nd level cache. But is this still true?

2. HQL does invalidate only a the 2nd level cache region which is related to the entity you are doing some inserts/updates/deletes on. That makes sense because Hibernate knows which entities are affected by the HQL, it can clear only the 2nd level cache region for this entity.

Example:

entityManager.createQuery("delete from Person p where p.id = 1").executeUpdate();

This will invalidate "only" the Person entity cache.

I am not aware of any possibility to prevent Hibernate from invalidating 2nd level cache for specific entity when it comes to HQL.

Answer 2

The closest thing I could dig up was this: http://docs.jboss.org/hibernate/core/3.3/reference/en/html/performance.html#performance-cache

I would imagine it has a lot to do with which provider you use.

Answer 3

We did see HQL update clearing the 2nd level cache when running with Hibernate 3.2.x

As a simple way to validate for your individual setup, implement something like:

http://narcanti.keyboardsamurais.de/hibernate-statistics-jsp-reloaded.html

Note details on that page before and after running the HQL update transaction ...

Or gather stats directly in your code and/or using JMX

http://docs.jboss.org/hibernate/core/3.5/reference/en/html/performance.html#performance-monitoring

As for improved behaviour, the Hibernate project might be open to implement a patch :)