Hi,
We are seeing class loading blocks coming from Hibernate classes, thread dump below -
Please can you advise in what cases it could happen? Any pointers? Thanks

3XMTHREADINFO1 (native thread ID:0x32B0061, native priority:0x3, native policy:UNKNOWN)
4XESTACKTRACE at java/lang/ClassLoader.loadClass(ClassLoader.java:609(Compiled Code))
4XESTACKTRACE at org/hibernate/util/ReflectHelper.classForName(ReflectHelper.java:118(Compiled Code))
4XESTACKTRACE at org/hibernate/impl/SessionFactoryImpl.getImportedClassName(SessionFactoryImpl.java:761(Compiled Code))
4XESTACKTRACE at org/hibernate/hql/QuerySplitter.getImportedClass(QuerySplitter.java:155(Compiled Code))
4XESTACKTRACE at org/hibernate/hql/QuerySplitter.concreteQueries(QuerySplitter.java:121(Compiled Code))
4XESTACKTRACE at org/hibernate/engine/query/HQLQueryPlan.<init>(HQLQueryPlan.java:92(Compiled Code))
4XESTACKTRACE at org/hibernate/engine/query/HQLQueryPlan.<init>(HQLQueryPlan.java:80(Compiled Code))
4XESTACKTRACE at org/hibernate/engine/query/QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:87(Compiled Code))
4XESTACKTRACE at org/hibernate/impl/AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:156(Compiled Code))
4XESTACKTRACE at org/hibernate/impl/AbstractSessionImpl.createQuery(AbstractSessionImpl.java:135(Compiled Code))
4XESTACKTRACE at org/hibernate/impl/SessionImpl.createQuery(SessionImpl.java:1650(Compiled Code))
4XESTACKTRACE at sun/reflect/GeneratedMethodAccessor263.invoke(Bytecode PC:42(Compiled Code))
4XESTACKTRACE at sun/reflect/DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37(Compiled Code))
4XESTACKTRACE at java/lang/reflect/Method.invoke(Method.java:578(Compiled Code))
4XESTACKTRACE at org/hibernate/context/ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:342(Compiled Code))
4XESTACKTRACE at $Proxy20.createQuery(Bytecode PC:18(Compiled Code))

I guess your java virtual machine need more memory either in heap or in perm-gen.
Try to increase -Xmx and -XX:MaxPermSize vm-paramaeter values for example:

-Xmx512m
-XX:MaxPermSize=256m