Question

I configured Second Level Cache using Ehcache in hibernate.cfg.xml ,ehcache.xml.And setting the cache-usage property in mapping files.And tyring to check the data is loaded from cache or db using hibenrate statices.But its not loaded.Its again execute the query.I mentioned code

<hibernate-configuration>
<session-factory>
    <property name="connection.username">pension2</property>
    <property name="connection.password">pension2</property>
    <property name="connection.url">jdbc:oracle:thin:@191.161.0.25:1521:pension</property>
    <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
    <property name="dialect">org.hibernate.dialect.OracleDialect</property>
    <property name="myeclipse.connection.profile">pension</property>
    <property name="show_sql">true</property>
    <property name="format_sql">true</property>
    <property name="use_sql_comments">true</property>

    <property name="hibernate.cache.use_second_level_cache">true</property>
    <property name="hibernate.generate_statistics">true</property>
    <property name="hibernate.cache.region.provider_class">
         net.sf.ehcache.hibernate.EhCacheProvider</property>
    <property name="hibernate.cache.provider_configuration_file_resource_path">/ehcache.xml </property>      
    <mapping resource="com/aims/mapping/Teacher.hbm.xml" />
    <mapping resource="com/aims/mapping/Student.hbm.xml" />
    <mapping resource="com/aims/mapping/Student_marks_detl.hbm.xml" />
    <mapping resource="com/aims/mapping/User.hbm.xml" />

</session-factory>
</hibernate-configuration>

ehcache.xml

    <ehcache> 
    <diskStore path="java.io.tmpdir"/> 
     <cache name="com.aims.beans.Teacher" 
    maxElementsInMemory="300" 
    eternal="false" 
    overflowToDisk="false"/> 
    </ehcache>

Mapping.xml

<hibernate-mapping>
<class name="com.aims.beans.Teacher" table="teacher">
<cache usage="read-write" />
<id name="tno" column="tno" type="java.lang.Integer" >
    <generator class="assigned" />
</id>
<property name="tname" type="java.lang.String" column="tname"/>
</class> 
</hibernate-mapping>

I trying to load teachers list in my jsp.So,Iam using createquery and setCacheable is true.

long oldHitCount = HibernateUtil.getHitCount();
long oldMissCount = HibernateUtil.getMissCount();
log.info(“oldHitCount” +oldHitCount + “oldMissCount”+ oldMissCount );
Query q = session.createQuery(“from Teacher”);
q.setCacheable(true);
list = q.list();
long newHitCount = HibernateUtil.getHitCount();
long newMissCount= HibernateUtil.getMissCount();

HibernateUtil.getHitCount()/HibernateUtil.getMissCount() Code

public static long getHitCount() {
        long hitcount = 0;
        hitcount = sessionFactory.getStatistics()
                .getSecondLevelCacheStatistics("com.aims.beans.Teacher")
                .getHitCount();
        return hitcount;
    }

    public static long getMissCount() {
        long miscount = 0;
        miscount = sessionFactory.getStatistics()
                .getSecondLevelCacheStatistics("com.aims.beans.Teacher")
                .getMissCount();
        return miscount;
    }

But every time execute the createQuery.I configured and every thing why its not returned from the cache.Is there any mistake to configure the second level cache.Please help me>?

Answer 1

The second level cache maps ids to entities, so it is only used when entities are queried by id. The query cache maps queries to a set of entity ids retrieved by the query. So the second level cache and query cache are actually only helpful when used together.

To enable the query cache it is not enough to set the query cacheable but you must also enable the query cache in your Hibernate session-factory configuration:

<property name="hibernate.cache.use_query_cache">true</property>

Hope this helps.