如何解决未显式加锁却频繁抛出PessimisticLockingFailureException的问题

异常背景 #

相关异常堆栈如下：

org.springframework.dao.PessimisticLockingFailureException: could not execute statement; SQL [n/a]; nested exception is org.hibernate.PessimisticLockException: could not execute statement
    at org.springframework.orm.hibernate5.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:240) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.orm.hibernate5.HibernateTransactionManager.convertHibernateAccessException(HibernateTransactionManager.java:804) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.orm.hibernate5.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:639) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:743) ~[spring-tx-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:711) ~[spring-tx-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:633) ~[spring-tx-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:386) ~[spring-tx-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:118) ~[spring-tx-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95) ~[spring-aop-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at com.sun.proxy.$Proxy168.delete(Unknown Source) ~[?:?]

对应的业务代码如下：

class Suppress {
Job job = serviceImpl.getJob(jobId);
String name = job.getJobName();
//do something with name
serviceImpl.delete(job)
}

@Transactional(propagation = Propagation.REQUIRED, readOnly = true, rollbackFor = Throwable.class)
class ServiceImpl{
getJob(int id){
    daoImpl.get(id)
}

delete(Job job){
   daoImpl.delete(job)
}
}

根因分析 #

• 事务配置错误：ServiceImpl类上标注了readOnly = true的全局事务配置，delete方法未单独指定事务属性，继承了只读配置。删除属于写操作，运行在只读事务中时，数据库无法分配写锁，和其他持有该行读锁的事务产生冲突触发异常。
• 事务边界拆分不合理：Suppress类中先后调用getJob、delete两个独立事务方法，第一个只读事务加载Job对象后会提交并释放读锁，第二个删除事务需要重新申请写锁，两个事务的间隙内如果有其他事务修改、锁定了对应行记录，就会触发锁冲突。
• 实体状态异常：第一个事务加载的Job对象在事务提交后变为游离态，delete方法执行时需要先将游离态实体重新关联到持久化上下文，关联过程中如果遇到行锁占用、版本冲突也会触发锁异常。

解决方案 #

• 修正事务属性配置：给delete方法单独添加事务注解，覆盖类级别的只读配置，保证写操作运行在可写事务中：

  @Transactional(propagation = Propagation.REQUIRED, readOnly = false, rollbackFor = Throwable.class)
  delete(Job job){
     daoImpl.delete(job)
  }
  

• 合并事务边界：将查询、操作、删除的逻辑封装到同一个事务中执行，避免两个独立事务之间的锁间隙被其他请求抢占。可以在ServiceImpl中新增组合方法，或者在外层调用逻辑上加事务注解，保证整个操作链路在同一个事务内完成。
• 显式配置锁策略：如果存在较高并发修改同一条Job记录的场景，可以在查询阶段就显式申请悲观写锁，避免后续执行写操作时出现锁冲突：

  getJob(int id){
      daoImpl.get(id, LockModeType.PESSIMISTIC_WRITE)
  }
  

• 新增重试机制：针对偶发的锁冲突，可以给删除逻辑添加3-5次的有限重试，捕获PessimisticLockingFailureException后间隔100-300ms再重试，提升并发场景下的操作成功率。

内容的提问来源于stack exchange，提问作者Hemanth