java - Hibernate 中的最大并发事务数是否有限制？

Question

我有一个客户端向使用 Hibernate 的服务层发送 3 个请求。

每个请求都会导致 Hibernate 开始一个事务 (session.beginTransaction())。

我发现，有时，一个事务(来自 2 个以上正在运行的并发事务)会失败，并显示createQuery is not valid without active transaction。

这是我使用的 Hibernate 配置(在 Tomcat 6.0.x 和 OC4j 10.1.3.4 中运行):

<property name="hibernate.connection.pool_size">5</property>
        <!--  <property name="hibernate.current_session_context_class">thread</property> -->
        <property name="hibernate.current_session_context_class">org.hibernate.context.ThreadLocalSessionContext</property>
        <property name="connection.autoReconnect">true</property>
        <property name="connection.autoReconnectForPools">true</property>
        <property name="connection.is-connection-validation-required">true</property>
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">false</property>

        <!-- auto commit -->
        <!-- <property name="connection.autocommit">true</property> -->

        <!-- configuration pool via c3p0 -->
        <property name="c3p0.idleConnectionTestPeriod">1000</property>
        <property name="c3p0.initialPoolSize">5</property>
        <property name="c3p0.maxPoolSize">10</property>
        <property name="c3p0.maxIdleTime">1</property>
        <property name="c3p0.maxStatements">30</property>
        <property name="c3p0.minPoolSize">1</property>

        <property name="cache.use_query_cache">true</property>
        <property name="cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
        <property name="cache.use_second_level_cache">true</property>

编辑:我使用以下代理来管理所有事务:

import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Logger;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;


/**
 * http://stackoverflow.com/questions/2587702
 * 
 * @author mohammad_abdullah
 */
public class ServiceProxy implements InvocationHandler {

    private Object object;
    private Logger logger = Logger.getLogger(this.getClass().getSimpleName());
    private static final String SESSION_FIELD = "session";

    public static final Map<Long, Transaction> ACTIVE_TRANSACTIONS = new HashMap<Long, Transaction>();

    private ServiceProxy(Object object) {
        this.object = object;
    }

    public static Object newInstance(Object object) {
        return Proxy.newProxyInstance(object.getClass().getClassLoader(), object.getClass().getInterfaces(), new ServiceProxy(object));
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Object result = null;
        Session session = null;
        boolean joined = false;
        try {
            if (Modifier.isPublic(method.getModifiers())) {

                session = HibernateUtil.getSessionFactory().getCurrentSession();

                Field sessionField = object.getClass().getSuperclass().getDeclaredField(SESSION_FIELD);
                if (sessionField == null)
                    throw new UPSAdminException("Service Implementation should have field named: \"" + SESSION_FIELD + "\".");
                sessionField.setAccessible(true);
                sessionField.set(object, session);

                if (session.getTransaction().isActive()) {
                    joined = true;
                    logger.info("Using Already Active transaction" + " Method: " + method.getName() + " Thread: "
                            + Thread.currentThread().getId());
                    ACTIVE_TRANSACTIONS.put(Thread.currentThread().getId(), session.getTransaction());
                } else {
                    logger.info("Transaction Began" + " Method: " + method.getName() + " Thread: " + Thread.currentThread().getId());
                    Transaction newTnx = session.beginTransaction();
                    ACTIVE_TRANSACTIONS.put(Thread.currentThread().getId(), newTnx);
                }
                result = method.invoke(object, args);

                if (!joined) {
                    ACTIVE_TRANSACTIONS.get(Thread.currentThread().getId()).commit();
                    ACTIVE_TRANSACTIONS.remove(Thread.currentThread().getId());
                    logger.info("Transaction Commited" + " Method: " + method.getName() + " Thread: " + Thread.currentThread().getId());
                }
            } else {
                result = method.invoke(object, args);
            }

            return result;

        } catch (InvocationTargetException _ex) {
            Throwable cause = _ex.getCause();
            logger.severe("Caller Exception: " + cause + " Method: " + method.getName() + " Thread: " + Thread.currentThread().getId());

            if (!joined && session != null && session.getTransaction().isActive()) {
                ACTIVE_TRANSACTIONS.get(Thread.currentThread().getId()).rollback();
                ACTIVE_TRANSACTIONS.remove(Thread.currentThread().getId());
            }

            if (cause instanceof HibernateException) {
                logger.severe("Hibernate Error. Rollbacked Back. Method: " + method.getName() + " Thread: "
                        + Thread.currentThread().getId());
                throw new DBException(cause.getCause().getMessage());

            } else if (cause instanceof SetRollbackException) {
                logger.severe("Transaction marked for Rollback. Rollbacked Back. Method: " + method.getName() + " Thread: "
                        + Thread.currentThread().getId());
                return result;

            } else {
                logger.severe("Error in Business Method : " + method + ". Rollbacked Back." + " Thread: " + Thread.currentThread().getId());
                throw cause;
            }
        } catch (Exception ex) {
            logger.severe("Error in Proxy code :" + ex + " Method :" + method + " Thread: " + Thread.currentThread().getId());

            if (!joined && session != null && session.getTransaction().isActive()) {
                ACTIVE_TRANSACTIONS.get(Thread.currentThread().getId()).rollback();
                ACTIVE_TRANSACTIONS.remove(Thread.currentThread().getId());
            }

            if (ex instanceof HibernateException)
                throw new DBException(ex.getCause().getMessage());

            throw ex;
        }
    }
}

Answer 1

由于您已经创建了大小为 5 的连接池，因此对于并发事务来说，它的运行应该不会出现太多问题。 createQuery() 方法更新脏持久性对象，它需要在事务内运行。我认为这就是您错误的原因。

说到事务和连接，每个事务都必须持有一个连接，但由于连接是池化的，如果事务处于等待状态，它会将连接释放回池中。如果并发事务太多而连接数量较少，则会延迟处理。对于长事务，甚至有可能出现死锁等问题......

您可以找到 transaction 的 hibernate API和 Contextual sessions在链接中。