Hibernate & lt; Level 2 Cache & gt; and hibernate Level 2 Cache

Hibernate <second-level cache> and hibernate second-level cache

Secondary cache:

Definition:

1. The second-level cache is called the process-level cache or sessionFactory-level cache. The second-level cache can be shared by all sessions.

2. the life cycle of the second-level cache is the same as that of sessionFactory (sessionFactory needs to be set in configuration). sessionFactory can manage the second-level cache.

3. the data in the second-level cache is put into the first-level cache. That is to say, the second-level cache is the same as that in the first-level cache. It is also a storage object and does not execute a cache policy on common attributes, the difference is that the second-level cache can share different lifecycles.

 

The second-level cache must be configured to take effect:

1. Introduce a third-party package ehcache

2. Configure in hibernate. cfg:

We need to configure three parts: one is provided by the driver, the other is to enable the second-level cache, and the third is to configure the entity class to be cached.

1 <! -- Level 2 cache driver provided --> 2 <property name = "hibernate. cache. provider_class"> org. hibernate. cache. EhCacheProvider </property> 3 <! -- Level 2 cache --> 4 <property name = "hibernate. cache. use_second_level_cache"> true </property> 5 6 <! -- Cache configuration --> 7 <class-cache usage = "read-only" class = "entity. Grade"/> 8 <! -- The object associated with grade --> 9 <class-cache usage = "read-only" class = "entity. student "/> 10 <collection-cache usage =" read-only "collection =" entity. grade. stu "/>

 

Note:

1. Because hibernate. cache. use_second_level_cache is enabled by default, we can also omit it.

2. Common cache policies: read-only/read-write

3. cache principle: Use cache when reading is much larger than writing

 

When Level 2 cache is enabled in configuration:

When the service does not need second-level cache:

HibernateUtils. getSessionFactory. evict (object. class );

Or

HibernateUtils. getSessionFactory. evict (object. class, 1); // specify a specific object

When we do not want the query results to be saved to the second-level cache:

Session. setCacheMode (CacheMode. IGNRE); // cancel the interaction between the level-1 cache and the level-2 cache, so that the current sesison cannot store data in the level-2 cache.

Supplement:

I mentioned in my notes yesterday that big data cache processing. When we enable the second-level cache, session. flush () session. clear () can only clear session-level caches. How to Handle sessionFactory-level/second-level caches:

Here I learned a method in the video:

Cancel the interaction between Level 1 cache and level 2 cache before saving or this query.