[DBCP-294] Memory leak in XA Implementation

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.3, 1.4, 2.0
• Fix Version/s: 1.3

Environment

JDK5, Oracle 10G,Postgres 8.x

• Assignee: Phil Steitz
• Reporter: Philippe Mouawad
• Created: 12/Jun/09 13:47
• Updated: 15/Feb/10 02:22
• Resolved: 25/Oct/09 16:28

Description

Hello,
We are been using Ofbiz with DBCP based implementation.
Ofbiz uses a Head revision of DBCP (package org.apache.commons.dbcp.managed is the same as current TRUNK) and geronimo-transaction-1.0.

We are having recurrent OutOfMemory which occur on a 2 days basis.
I analyzed the Heap Dump and I think have found the source of the problem:
The Heap Dump shows a Retained Heap of 400Mo by org.apache.commons.dbcp.managed.TransactionRegistry#xaResources field.

After analyzing more deeply, the leak seems to come from what is stored in xaResources through
xaResources.put(connection, xaResource);

Values inside weak Hash map will never be removed since XAResource holds a STRONG reference on key (connection) through:
org.apache.commons.dbcp.managed.LocalXAConnectionFactory$LocalXAResource through:
public LocalXAResource(Connection localTransaction)

{ this.connection = localTransaction; }

Found in WeakHashMap javadoc:
Implementation note: The value objects in a WeakHashMap are held by ordinary strong references. >>>>>>>>>>>>>Thus care should be taken to ensure that value objects do not strongly refer to their own keys <<<<<<<<, either directly or indirectly, since that will prevent the keys from being discarded. Note that a value object may refer indirectly to its key via the WeakHashMap itself; that is, a value object may strongly refer to some other key object whose associated value object, in turn, strongly refers to the key of the first value object. One way to deal with this is to wrap values themselves within WeakReferences before inserting, as in: m.put(key, new WeakReference(value)), and then unwrapping upon each get.

Philippe Mouawad
http://www.ubik-ingenierie.com