[jbosscache-issues] [JBoss JIRA] Updated: (JBCACHE-1557) EvictionTimer thread going into endless loop when using LFUAlgorithm

EvictionTimer thread going into endless loop when using LFUAlgorithm -------------------------------------------------------------------- Key: JBCACHE-1557 URL: https://jira.jboss.org/jira/browse/JBCACHE-1557 Project: JBoss Cache Issue Type: Bug Security Level: Public(Everyone can see) Components: Eviction Affects Versions: 3.2.1.GA Environment: Hibernate3.3.2GA using JBOSSCACHE3.2.1GA as second level cache implementation Database: SQLServer2008 Reporter: Guenther Demetz Assignee: Manik Surtani Background:Im using JBoss-cache 3.2.1 GA as 2L-cache for a Hibernate application. As Hibernate documentation does not suggest LRU as algorithm for 2L-cache, I use the LFU algorithm. At a certain point BaseEvictionAlgorithm#prune method never exits his loop anymore because of evictionQueue.getFirstNodeEntry() always returning the same value. Debugging the code we saw that the actual bug stays in method LFUQueue#removeNodeEntry (see code below) : This method don't handles correctly the case of non-existance of the node in the nodeMap: if ne == null, then neither removalQueue nor the evictionList is touched. This causes evictionQueue.getFirstNodeEntry() returning always the same result. Code: BaseEvictionAlgorithm.java ... protected void prune() throws EvictionException { NodeEntry entry; while ((entry = evictionQueue.getFirstNodeEntry()) != null) --> ENDLESS-LOOP because evict doesn't alter the evictionQueye { if (this.shouldEvictNode(entry)) { this.evict(entry); } else { break; } } } Code: LFUQueue.java: public void removeNodeEntry(NodeEntry entry) { NodeEntry ne = nodeMap.remove(entry.getFqn()); if (ne != null) { // don't remove directly from the LinkedList otherwise we will incur a O(n) = n // performance penalty for every removal! In the prune method for LFU, we will iterate the LinkedList through ONCE // doing a single O(n) = n operation and removal. This is much preferred over running O(n) = n every single time // remove is called. There is also special logic in the getFirstNodeEntry that will know to check // the removalQueue before returning. this.removalQueue.add(ne); /* if(!evictionList.remove(ne)) { throw new RuntimeException(""); } */ this.numElements -= ne.getNumberOfElements(); } } Solution: following Else-block added in method LFUQueue#removeNodeEntry resolves the problem. Code: else { // ELSE BLOCK: bugfix: this prevents endless loop in BaseEvictionAlgorithm#prune method if(!evictionList.remove(entry)) throw new RuntimeException(""); this.removalQueue.add(entry); this.numElements -= entry.getNumberOfElements(); } N.B.: In other parts of the code, i.e BaseEvictionAlgorithm: line 406 the non-existance of the node is properly handled, see following logging outputs: 13:55:11,712 DEBUG BaseEvictionAlgorithm:384 - Removing node /com/wuerth/phoenix/Cis/bc/persistent/jpa/ConcreteAccountPeer/assAccount/COLL/com.wuerth.phoenix.Cis.bc.persistent.jpa.ConcreteAccountPeer.assAccount#32770 from eviction queue and attempting eviction 13:55:11,712 DEBUG BaseEvictionAlgorithm:406 - processRemoveNodes(): Can't find node associated with fqn: /com/wuerth/phoenix/Cis/bc/persistent/jpa/ConcreteAccountPeer/assAccount/COLL/com.wuerth.phoenix.Cis.bc.persistent.jpa.ConcreteAccountPeer.assAccount#32770Could have been evicted earlier. Will just continue. regards G.D.