Have a table temp .. Code:

CREATE TABLE `temp` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `student_id` bigint(20) unsigned NOT NULL,
  `current` tinyint(1) NOT NULL DEFAULT  1 ,
  `closed_at` datetime NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `unique_index` (`student_id`,`current`,`closed_at`),
  KEY `studentIndex` (`student_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

相应的Java pojo是http://pastebin.com/JHZwubWd。此表具有唯一的约束，因此每个学生只能有一条记录处于活动状态。

2) I have a test code which does try to continually add records for a student ( each time making the older active one as inactive and adding a new active record) and also in a different thread accessing some random ( non-related ) table. Code:

public static void main(String[] args) throws Exception {
        final SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
        ExecutorService executorService = Executors.newFixedThreadPool(1);
        int runs = 0;
        while(true) {
            Temp testPojo = new Temp();
            testPojo.setStudentId(1L);
            testPojo.setCurrent(true);
            testPojo.setClosedAt(new Date(0));
            add(testPojo, sessionFactory);
            Thread.sleep(1500);

            executorService.submit(new Callable<Object>() {
                @Override
                public Object call() throws Exception {
                    Session session = sessionFactory.openSession();
                    // Some dummy code to print number of users in the system.
                    // Idea is to "touch" the DB/session in this background
                    // thread.
                    System.out.println("No of users: " + session.createCriteria(User.class).list().size());
                    session.close();
                    return null;
                }
            });
            if(runs++ > 100) {
                break;
            }
        }

        executorService.shutdown();
        executorService.awaitTermination(1, TimeUnit.MINUTES);
    }

private static void add(final Temp testPojo, final SessionFactory sessionFactory) throws Exception {
        Session dbSession = null;
        Transaction transaction = null;
        try {
            dbSession = sessionFactory.openSession();
            transaction = dbSession.beginTransaction();

            // Set all previous state of the student as not current.
            List<Temp> oldActivePojos = (List<Temp>) dbSession.createCriteria(Temp.class)
                    .add(Restrictions.eq("studentId", testPojo.getStudentId())).add(Restrictions.eq("current", true))
                    .list();
            for(final Temp oldActivePojo : oldActivePojos) {
                oldActivePojo.setCurrent(false);
                oldActivePojo.setClosedAt(new Date());

                dbSession.update(oldActivePojo);
                LOG.debug(String.format("  Updated old state as inactive:%s", oldActivePojo));
            }
            if(!oldActivePojos.isEmpty()) {
                dbSession.flush();
            }

            LOG.debug(String.format("  saving state:%s", testPojo));
            dbSession.save(testPojo);
            LOG.debug(String.format("  new state saved:%s", testPojo));

            transaction.commit();

        }catch(Exception exception) {
            LOG.fatal(String.format("Exception in adding state: %s", testPojo), exception);
            transaction.rollback();
        }finally {
            dbSession.close();
        }
    }

在运行代码时，经过几次运行，我得到了一个索引约束异常。之所以会发生这种情况，是因为出于某种奇怪的原因，它没有找到最新的活动记录，而是找到了一些旧的过时活动记录，并试图在保存之前将其标记为非活动记录（尽管DB实际上已经有了新的活动记录）。

请注意，这两个代码共享同一个会话工厂，并且这两个编码在完全不同的表上工作。我的猜测是某些内部缓存状态变脏了。如果我使用两个不同的会话工厂作为前台和后台线程，它工作得很好。

另一件奇怪的事情是，在后台线程中（我在其中打印用户编号），如果我将其封装在事务中（即使这只是一个读取操作），代码运行良好！Sp看起来我需要将所有DB操作（无论读/写）封装在事务中，以便它在多线程环境中工作。

有人能指出这个问题吗？