Question

我有两个运行相同代码的应用程序，在hibernate的帮助下查询同一个Oracle数据库有一个表可以保存要发送的电子邮件这两个应用程序都运行一个调度程序，用于查询此表中的列以查找＆＃34; QUEUED＆＃34; string（标记要发送的电子邮件），创建和发送电子邮件，最后更新，＆＃34; QUEUED＆＃34;到＆＃34; SENT＆＃34;所以这些电子邮件不会再被发送理论上，我希望一个应用程序读取一些行，锁定它们的读写，更新它们并解锁以供另一个应用程序使用。
因此我使用以下查询：

String jpql = "SELECT m FROM Email m WHERE m.status = :status";
return em.createQuery(jpql, Email.class)
        .setParameter("status", "QUEUED")
        .setLockMode(LockModeType.PESSIMISTIC_WRITE)
        .getResultList();

由应用程序和文档使用，LockModeType.PESSIMISTIC_WRITE相当于＆＃34; SELECT FOR UPDATE＆＃34;。
相反，以下行为发生：

13:06:02,160 | MailQueueMonitor_1| Found 0 email(s) to be sent. // No rows returned from app1  

13:06:03,813 | MailQueueMonitor_2| Found 0 email(s) to be sent. // No rows returned from app2  

13:06:12,180 | MailQueueMonitor_1| Found 1 email(s) to be sent. // 1 mail returned from app1  

13:06:12,190 | MailQueueMonitor_1| Mailer will sleep for 30s    // App1 will sleep for 30s   

// At this point, app2 tries to execute query but freezes as app1 has the keys to the rows  

13:06:42,191 | MailQueueMonitor_1| Mailer woke up and will try to send mails    // App1 wakes up  

13:06:46,796 | MailQueueMonitor_1| Mailer sent mail     // App1 sent mail  

13:06:46,798 | MailQueueMonitor_1| Mailer changed mail status to SENT // App1 update status from QUEUED to SENT  

// At this point, app1 releases the locks and app2 unfreezes and executes query looking for QUEUED rows which should not exist at this point since they where updated to SENT.  

13:06:46,809 | MailQueueMonitor_2| Found 1 email(s) to be sent. // App2 queries and finds 1 row! It is like it queried a snapshot of the database before app2 updated all rows.  

13:06:46,836 | MailQueueMonitor_2| Mailer will sleep for 30s    // App2 will sleep for 30s  

13:07:16,836 | MailQueueMonitor_2| Mailer woke up and will try to send mails    // App2 wakes up  

13:07:21,457 | MailQueueMonitor_2| Mailer sent mails    // App2 sent mail. This is re-senting above email occuring to duplicate emails.  

13:07:21,458 | MailQueueMonitor_2| Mailer changed mail status SENT  // App2 update status from QUEUED to SENT, again!

问题是，为什么app2不会读取更新的行，即使在锁定释放后执行查询。为什么app2尝试查询锁定的行时不会抛出异常？我应该如何锁定行被读取或更新，并且在锁定释放后，将查询数据库的下一个应用程序将看到更新的数据？

一些注意事项：
1.如果我在两个连续的行上运行查询两次，当锁被释放时，先前锁定的应用程序将执行第一个查询（这是被锁定的一个）将返回未更新的数据，但第二个将返回应用程序的更新数据以前有过锁 2.如果我通过两个ORACLE SQL DEVELOPER实例手动运行上述过程，则行为符合预期，即：

SQL_DEV_1: SELECT * FROM T_MAIL WHERE STATUS = 'QUEUED' FOR UPDATE; // Returns 1 row, locks the row
SQL_DEV_2: SELECT * FROM T_MAIL WHERE STATUS = 'QUEUED' FOR UPDATE; // Doesn't return anything but keeps waiting for locks to be released
SQL_DEV_1: UPDATE T_MAIL SET STATUS = 'SENT'; // Returns 1 row, locks the row
SQL_DEV_1: COMMIT; // Commit update, locks are released
SQL_DEV_2: // waiting query is executed, returns no rows since one and only row was update to SENT

Answer 1

我认为我找到了解决方案（或解决方法）。当您使用PESSIMISTIC_WRITE时，第二个服务器不知道第一个服务器正在更改数据。在使用LockModeType.PESSIMISTIC_READ时，他可以了解这一点，但在LockModeType.PESSIMISTIC_READ中使用LockModeType.PESSIMISTIC_WRITE实现了version。因此，针对您的解决方法是将LockModeType.PESSIMISTIC_FORCE_INCREMENT字段和设置模式添加到library(ggplot2) dat = data.frame(x=c(0,100), ymin=0, y=c(100,0), ymax=100) ggplot(dat) + geom_ribbon(aes(x, ymin=y, ymax=ymax), fill="blue") + geom_ribbon(aes(x, ymin=ymin, ymax=y), fill="red") + geom_abline(aes(intercept=100, slope=-1)) + #geom_line(aes(x,y), lwd=1) + # If you just want a line with the same extent as the data theme_bw()

JPA LockModeType.PESSIMISTIC_WRITE没有按预期工作。没有密钥的应用程序，在锁定

1 个答案: