A Quick note about Hibernate Caching
1) First Level Cache (Transaction Layer)
a) Associated with a Hibernate Session (transaction scoped) and this cache is used by Hibernate transparently. Hibernate requires a key to load object from the session cache. Hence its better to call a load() or get(), when the key(EntityKey) is known, rather than using a HQL query.
b) All queries (state of an entity, updates) in the cache gets flushed / committed to the database only when Transaction context ends (i.e.) getTransaction().commit is called.
c) Always used and cannot be turned off.
2) Second Level Cache (Application Layer)
a) Associated with a Hibernate’s SessionFactory (process scoped). Enabled by default in Hibernate 3 and uses EHCache as default cache provider.
b) The cache entries are dehydrated states of entity objects. A dehydrated state of entity refers to a key-value pair where key is the entity id (of the dehydrated entity) and the set of (deep copy) of attributevalues (dehydrated entity fields) refer to the value. Hibernate does not cache associations in a dehydrated object by default. One has to manually configured which association in a dehydratable entity to be cached.
Syntax : { id > { atribute1, attribute2, attribute3,{attribute41, attribute42},… } }
3) Query cache (org.hibernate.cache.QueryCache)
a) Defines 2 cache regions : org.hibernate.cache.StandardQueryCache (stores query with parameters as cache key) and org.hibernate.cache.UpdateTimestampsCache (keeps stale query results of last results fetch). Both the cache regions are evicted when the entity related to the cacheable query is updated.
Syntax : { query,{parameters}} —> {id of cached entity}
b) A specific query results are cached, by specifying setCacheable(true) on Session’s Query handle.
1) First Level Cache (Transaction Layer)
a) Associated with a Hibernate Session (transaction scoped) and this cache is used by Hibernate transparently. Hibernate requires a key to load object from the session cache. Hence its better to call a load() or get(), when the key(EntityKey) is known, rather than using a HQL query.
b) All queries (state of an entity, updates) in the cache gets flushed / committed to the database only when Transaction context ends (i.e.) getTransaction().commit is called.
c) Always used and cannot be turned off.
2) Second Level Cache (Application Layer)
a) Associated with a Hibernate’s SessionFactory (process scoped). Enabled by default in Hibernate 3 and uses EHCache as default cache provider.
b) The cache entries are dehydrated states of entity objects. A dehydrated state of entity refers to a key-value pair where key is the entity id (of the dehydrated entity) and the set of (deep copy) of attributevalues (dehydrated entity fields) refer to the value. Hibernate does not cache associations in a dehydrated object by default. One has to manually configured which association in a dehydratable entity to be cached.
Syntax : { id > { atribute1, attribute2, attribute3,{attribute41, attribute42},… } }
3) Query cache (org.hibernate.cache.QueryCache)
a) Defines 2 cache regions : org.hibernate.cache.StandardQueryCache (stores query with parameters as cache key) and org.hibernate.cache.UpdateTimestampsCache (keeps stale query results of last results fetch). Both the cache regions are evicted when the entity related to the cacheable query is updated.
Syntax : { query,{parameters}} —> {id of cached entity}
b) A specific query results are cached, by specifying setCacheable(true) on session’s Query handle.