hibernate与proxool连接池无法自动释放连接的问题

proxool的配置如下：
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop> 
                <prop key="hibernate.show_sql">false</prop> 
                <prop key="hibernate.connection.autocommit">true</prop>
<prop key="hibernate.connection.release_mode">after_statement</prop>            
                <prop key="hibernate.bytecode.use_reflection_optimizer">true</prop>
             <prop key="hibernate.connection.provider_class">org.hibernate.connection.ProxoolConnectionProvider</prop>
                <prop key="hibernate.proxool.xml">../config/proxool.xml</prop>
                <prop key="hibernate.proxool.pool_alias">biz_alias</prop>
                <!---->
</props>
</property>

如果启用了<prop key="hibernate.connection.release_mode">after_statement</prop> 然后代码里创建了Transaction的话，要将transaction.commit();否则无法自动释放连接，导致连接数被占用满而报错。