Hi,

I'm trying to add EhCache to a JPA and Hibernate project.

Below is my configuration.

persistence.xml:


<persistence-unit name="pollPersistenceUnit">
<properties>
<!-- 2nd level cache -->
<property name="hibernate.cache.provider_class"
value="net.sf.ehcache.hibernate.SingletonEhCacheProvider" />
<property name="hibernate.cache.provider_configuration" value="/ehcache.xml" />
<property name="hibernate.cache.use_second_level_cache"
value="true" />
<property name="hibernate.generate_statistics" value="true" />
<property name="hibernate.cache.use_structured_entries"
value="true" />
</properties>
</persistence-unit>


ehcache.xml:


<ehcache>
<diskStore path="java.io.tmp"/>
<defaultCache
maxElementsInMemory="10"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"/>
<cache name="se.aftonbladet.poll.bean.Poll"
maxElementsInMemory="10"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="180"
overflowToDisk="true"/>
</ehcache>



Poll class annotations:


@Entity
@Table(name = "poll")
@org.hibernate.annotations.Cache(usage =
org.hibernate.annotations.CacheConcurrencyStrategy.READ_WRITE
)
public class Poll implements Serializable {
...


I'm using Spring and here is my applicationContext.xml:


<bean
class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPost
Processor" />
<!-- pollManager and databaseInterface are our own Spring beans (from
Poll project) -->
<bean id="pollService" class="se.aftonbladet.poll.PollServiceManager">
<property name="pollDAO" ref="pollDAO"/>
</bean>

<beanid="pollDAO"class="se.aftonbladet.poll.JPAPollDAO">
</bean>

<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBea
n">
<property name="dataSource" ref="dataSource" />
<property name="persistenceUnitName" value="pollPersistenceUnit" />
<property name="jpaVendorAdapter">
<bean
class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="database" value="MYSQL" />
<property name="showSql" value="false" />
</bean>
</property>
</bean>
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="..." />
<property name="username" value="..." />
<property name="password" value="..." />
</bean>
<bean id="transactionManager"
class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<tx:annotation-driven transaction-manager="transactionManager" />
</beans>



I'm not really sure how to test if the cache is working. What would be the best way to do this?

Another thing I can't figure out is what the READ_WRITE CacheConcurrencyStrategy really means. Can I use EhCache for batch insertion into db? Or is it only used for caching beans read from db?

just enable some more logging for the correct packages,
you'll see the cache puts/hits/misses...

Aha, thanx!

Do you also know what the EhCache READ_WRITE configuration does?
I've tried to google it, but I can't seem to understand if EhCache can be used for batch insertion as well as caching beans read from db.

Also, does my configuration so far look OK to you?

looks good, but I don't know Spring, also I can't say about the caching options you selected as every application is different.


what do you mean? when you commit a transaction you want to have the entities flushed to disk, right? so what does a cache have to do with batch writing?

If you have have hibernate begin a transaction, then persist 100 entities, then commit or flush you will get 100 entities pushed to disk anyway, even without a cache.

Eh, ok I'm even more clueless now.;)

Flushed to disk - what does that mean? Sorry for being such a newbie. I understand that stuff actually gets done (visavi the database) when the transaction is over (or I call commit/flush explicitly).
What I would like to have is batch insertion. I thought maybe Ehcache could help me with this too. But you say that when the transaction is over (or I call commit/flush explicitly), then my entity/entities will be inserted into db - with or without Ehcache? And if I want to batch up a number of entities before actually inserting into database - then I have to make this happen in the code, before starting a new transaction?

/Håkan

don't worry, you're welcome to ask questions, if it's a bad one nobody will answer;-)

what I meant to say is that, (as far as I know) ehcache (nor any other caching solution) has anything to do with batch inserts.
You achieve the "batch performance" by persisting many (100? 1000? don't push it too much..) during the same transaction.

something like:
tx.begin();
for ( ...) {
persist();
}
tx.commit();

after that you can tweak many more settings, but caching is not really relevant (it could actually slow you down). you'll have to try settings, just remember to not have too big transactions.

Much clearer now - thanx a lot for your time and patience!

Hi again=)

I have the cache working fine now. Except for one problem.
I'm using query caching as well as second level caching.
I have two beans:

Poll
Answer

Poll has a collection of Answers.
I've added the collection as a cache region in the ehcache.xml.
I've annotated the collection (in the Poll class) with the proper annotation:

@org.hibernate.annotations.Cache(usage = org.hibernate.annotations.CacheConcurrencyStrategy.READ_WRITE)

I've used the setHint-method on the query where I retrive the Poll object and its Collection of answers:

List<Poll> polls = (List<Poll>)entityManager.createQuery("select distinct object(p) from Poll p INNER JOIN FETCH p.answers WHERE p.id = :id").setParameter("id", pollid).setHint(”org.hibernate.cacheable”, true).getSingleResult();


I try to retrieve a Poll object with its Answers twice to test the caching. First call is OK, I get my answers in the Poll object. But the second call fails with a LazyLoadInitialization exception (I'm calling getAnswers() outside of the transaction). The first call gets the Poll object from the database and the second call gets it from the cache.

Do you have an idea as to what may cause this?
(I have some logging of the cacheing and the Collection cache region is found.)

Sorry for the typo in the code showing the query. Should'nt be a List of Polls. Just Poll p = (Poll)entityManager...