Be aware that caches are not aware of changes made to the persistent store by another application. They can, however, be configured to regularly expire cached data. You have the option to tell Hibernate which caching implementation to use by specifying the name of a class that implements org. CacheProvider using the property hibernate. Hibernate is bundled with a number of built-in integrations with the open-source cache providers that are listed in Table You can also implement your own and plug it in as outlined above.
Note that versions prior to Hibernate 3. As we have done in previous chapters we are looking at the two different possibiltites to configure caching. First configuration via annotations and then via Hibernate mapping files. By default, entities are not part of the second level cache and we recommend you to stick to this setting.
However, you can override this by setting the shared-cache-mode element in your persistence. The following values are possible:. ALL : all entities are always cached even if marked as non cacheable. NONE : no entity are cached even if marked as cacheable. This option can make sense to disable second-level cache altogether.
The cache concurrency strategy used by default can be set globaly via the hibernate. The values for this property are:. It is recommended to define the cache concurrency strategy per entity rather than using a global one.
Use the org. Cache annotation for that. Definition of cache concurrency strategy via Cache. Hibernate also let's you cache the content of a collection or the identifiers if the collection contains other entities.
Use the Cache annotation on the collection property. Cache annotations with its attributes. It allows you to define the caching strategy and region of a given second level cache. Cache annotation with attributes. Let's now take a look at Hibernate mapping files. Looking at Example If your application needs to read, but not modify, instances of a persistent class, a read-only cache can be used.
This is the simplest and optimal performing strategy. It is even safe for use in a cluster. If the application needs to update data, a read-write cache might be appropriate. This cache strategy should never be used if serializable transaction isolation level is required.
If the cache is used in a JTA environment, you must specify the property hibernate. In other environments, you should ensure that the transaction is completed when Session. If you want to use this strategy in a cluster, you should ensure that the underlying cache implementation supports locking. The built-in cache providers do not support locking. If the application only occasionally needs to update data i.
If the cache is used in a JTA environment, you must specify hibernate. The transactional cache strategy provides support for fully transactional cache providers such as JBoss TreeCache.
Such a cache can only be used in a JTA environment and you must specify hibernate. The following table shows which providers are compatible with which concurrency strategies.
Whenever you pass an object to save , update or saveOrUpdate , and whenever you retrieve an object using load , get , list , iterate or scroll , that object is added to the internal cache of the Session. When flush is subsequently called, the state of that object will be synchronized with the database. If you do not want this synchronization to occur, or if you are processing a huge number of objects and need to manage memory efficiently, the evict method can be used to remove the object and its collections from the first-level cache.
Explcitly evicting a cached instance from the first level cache using Session. The Session also provides a contains method to determine if an instance belongs to the session cache.
To evict all objects from the session cache, call Session. For the second-level cache, there are methods defined on SessionFactory for evicting the cached state of an instance, entire class, collection instance or entire collection role. Second-level cache eviction via SessionFactoty.
The CacheMode controls how a particular session interacts with the second-level cache:. GET : will read items from the second-level cache. Do not write to the second-level cache except when updating data. PUT : will write items to the second-level cache. Do not read from the second-level cache. Bypass the effect of hibernate. To browse the contents of a second-level or query cache region, use the Statistics API:.
Browsing the second-level cache entries via the Statistics API. You will need to enable statistics and, optionally, force Hibernate to keep the cache entries in a more readable format:. Query result sets can also be cached. This is only useful for queries that are run frequently with the same parameters. Caching of query results introduces some overhead in terms of your applications normal transactional processing.
For example, if you cache results of a query against Person Hibernate will need to keep track of when those results should be invalidated because changes have been committed against Person. That, coupled with the fact that most applications simply gain no benefit from caching query results, leads Hibernate to disable caching of query results by default.
To use query caching, you will first need to enable the query cache:. StandardQueryCache , holding the cached query results. UpdateTimestampsCache , holding timestamps of the most recent updates to queryable tables.
These are used to validate the results as they are served from the query cache. If you configure your underlying cache implementation to use expiry or timeouts is very important that the cache timeout of the underlying cache region for the UpdateTimestampsCache be set to a higher value than the timeouts of any of the query caches.
In fact, we recommend that the the UpdateTimestampsCache region not be configured for expiry at all. Note, in particular, that an LRU cache expiry policy is never appropriate. As mentioned above, most queries do not benefit from caching or their results. So by default, individual queries are not cached even after enabling query caching. To enable results caching for a particular query, call org.
This call allows the query to look for existing cache results or add its results to the cache when it is executed.
The query cache does not cache the state of the actual entities in the cache; it caches only identifier values and results of value type. For this reaso, the query cache should always be used in conjunction with the second-level cache for those entities expected to be cached as part of a query result cache just as with collection caching. If you require fine-grained control over query cache expiration policies, you can specify a named cache region for a particular query by calling Query.
If you want to force the query cache to refresh one of its regions disregard any cached results it finds there you can use org. In conjunction with the region you have defined for the given query, Hibernate will selectively force the results cached in that particular region to be refreshed.
This is particularly useful in cases where underlying data may have been updated via a separate process and is a far more efficient alternative to bulk eviction of the region via org. Hibernate internally needs an entry org. EntityEntry to tell the current state of an object with respect to its persistent state, when the object is associated with a Session. However, maintaining this association was kind of heavy operation due to lots of other rules must by applied, since 4.
Basically, the idea is, instead of having a customized kind of heavy and which was usually identified as hotspot map to do the look up, we change it to. More info about org. ManagedEntity please find from its javadoc. Sometimes, you probably don't want to implement an intrusive interface, maybe due to portable concern, which is fine and Hibernate will take care of this internally with a wrapper class which implements that interface, and also an internal cache that maps this entity instance and the wrapper together.
Obviously, this is the easiest way to choose, since it doesn't require any change of the project source code, but it also cost more memory and CUP usage, comparing to the first one.
Besides the above two approaches, Hibernate also provides a third choice which is build time bytecode enhancement. Applications can use enhanced entity classes, annotated with either javax. Entity or composite javax. To use the task org. EnhancementTask define a taskdef and call the task, as shown below.
We can prefer this mode whenever we have less data in the collections. It will be faster while accessing the collections as its already loaded everything in one shot. This is best to use when we want faster response on accessing single entity. It loads additional data only when its required. In many places of our application,we may need only User details not the address details. Whenever we need addresses of an user in other parts of an application, It will be loaded only at that moment.
Example : When we have a batch processing of say 10 Users at a time. BatchSize of 10 will drastically reduces the number of queries required. Most important point to note here is, If batch size is small then its performance will be good otherwise it leads to more time and affect the performance.
We have to prefer this mode when we have small Batch size and have the requirement of processing the data batch wise. This should be used when we have an entity where most of them are loaded in the session. Most important point to note here is that all the collections are fetched even if the parent is not in the session.
Example: If we have users in the database and only few users are in the session then using SubSelect is not a good choice as it loads the addresses of all the users using sub query. We should prefer it when we have one entity whose most of the records are already loaded in the session. Note: Using the right fetching strategy based on our requirement is important to optimize the Hibernate query performance. If we use these strategies in a wrong way, then it will badly affect the performance of the query.
Tuplizers org. Tuplizer in Hibernate. EntityNameResolvers in Hibernate. Identity columns and sequences in Hibernate. Assigned identifiers in Hibernate. Primary keys assigned by triggers in Hibernate. Fetching strategies in Hibernate. Improve this question. M Sach M Sach Add a comment. Active Oldest Votes. Hibernate collections have fetch type and fetch mode settings.
See also: Fetching strategies. Improve this answer. Brad Cupit 6, 8 8 gold badges 55 55 silver badges 59 59 bronze badges. Amazing and quick clarification — M Sach. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
0コメント