@Override
public void clear() {
    EntityManager em = getEntityManager();
    Object newTx = joinTransaction(em);
    try {
        List<ProcessInstanceLog> processInstances = em.createQuery("FROM ProcessInstanceLog").getResultList();
        for (ProcessInstanceLog processInstance: processInstances) {
            em.remove(processInstance);
        }
        List<NodeInstanceLog> nodeInstances = em.createQuery("FROM NodeInstanceLog").getResultList();
        for (NodeInstanceLog nodeInstance: nodeInstances) {
            em.remove(nodeInstance);
        }
        List<VariableInstanceLog> variableInstances = em.createQuery("FROM VariableInstanceLog").getResultList();
        for (VariableInstanceLog variableInstance: variableInstances) {
            em.remove(variableInstance);
        }
    } finally {
    	closeEntityManager(em, newTx);
    }
}