[hibernate-issues] [Hibernate-JIRA] Closed: (HHH-1328) org.hibernate.util.SimpleMRUCache keeps a soft reference to the cache key, so cached values get collected prematurely

org.hibernate.util.SimpleMRUCache keeps a soft reference to the cache key, so cached values get collected prematurely --------------------------------------------------------------------------------------------------------------------- Key: HHH-1328 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1328 Project: Hibernate Core Issue Type: Bug Components: core Environment: Hibernate 3.1. I believe this hasn't changed in CVS. Reporter: Tzvetan Mikov Assignee: Steve Ebersole Priority: Minor Fix For: 3.1.1 org.hibernate.util.SimpleMRUCache uses org.apache.commons.collections.ReferenceMap to map HQLQueryPlanKey to HQLQueryPlan. However both the value and the key are stored with soft references. The last 128 HQLQueryPlan-s are kept in a strong reference array, but the cache keys aren't, so often cache entries cannot be found, even though the values still exist in memory. There is a comment in the source saying: // both keys and values may be soft since value keeps a hard ref to the key (and there is a hard ref to MRU values) but it isn't actually true since the value (HQLQueryPlan) doesn't actually keep a reference to the key (HQLQueryPlanKey). This is a simplistic patch that should fix the problem: --- SimpleMRUCache.java 2005-12-12 07:03:46.000000000 -0800 +++ SimpleMRUCache-new.java 2005-12-28 18:34:09.920112661 -0800 @@ -16,20 +16,24 @@ private static final int MAX_STRONG_REF_COUNT = 128; //TODO: configurable? private final transient Object[] strongRefs = new Object[MAX_STRONG_REF_COUNT]; //strong reference to MRU queries + private final transient Object[] strongKeyRefs = new Object[MAX_STRONG_REF_COUNT]; private transient int strongRefIndex = 0; private final transient Map softQueryCache = new ReferenceMap(ReferenceMap.SOFT, ReferenceMap.SOFT) ; - // both keys and values may be soft since value keeps a hard ref to the key (and there is a hard ref to MRU values) public synchronized Object get(Object key) { Object result = softQueryCache.get( key ); if( result != null ) { - strongRefs[ ++strongRefIndex % MAX_STRONG_REF_COUNT ] = result; + ++strongRefIndex; + strongRefs[ strongRefIndex % MAX_STRONG_REF_COUNT ] = result; + strongKeyRefs[ strongRefIndex % MAX_STRONG_REF_COUNT ] = key; } return result; } public void put(Object key, Object value) { softQueryCache.put( key, value ); - strongRefs[ ++strongRefIndex % MAX_STRONG_REF_COUNT ] = value; + ++strongRefIndex; + strongRefs[ strongRefIndex % MAX_STRONG_REF_COUNT ] = value; + strongKeyRefs[ strongRefIndex % MAX_STRONG_REF_COUNT ] = key; } }