java - 使用 OpenJPA 时 ORM 出现死锁

Question

使用 Soap UI 运行 10 个线程执行负载测试时，我遇到了死锁，每个线程向我的 Web 服务发出 10 个请求，该服务调用 OpenJPA 实体管理器的 persists 方法。

然后我执行单个请求，一切顺利，但在多线程环境中最终会出现死锁。

我收到的错误是:

Deadlock found when trying to get lock; try restarting transaction {prepstmnt 12796448 UPDATE Assessment SET dateCompleted = ? WHERE id = ? [params=?, ?]} [code=1213, state=40001]

因死锁而崩溃的方法是这样的:

@Override
public AssessmentKey update(AssessmentKey assessmentKey) {
    OpenJPAEntityManager openJpaEntityMgr = OpenJPAPersistence.cast(entityManager);
    for (Assessment assessment : assessmentKey.getAssessments()) {
        if (!entityManager.contains(assessment) && !openJpaEntityMgr.isDetached(assessment)) {
            LOGGER.debug("Persisting {}", assessment);
            entityManager.persist(assessment);
        }
    }
    return entityManager.merge(assessmentKey);
}

Assessment是OpenJPA的一个实体，它只是一个包含JPA注释的普通实体。如果您需要它的代码，请索要。

我了解了死锁是如何发生的，如何解决它们在here中提到。 。但是如何在 ORM 中解决它们我无法找到答案。

我的 persistence.xml 文件如下所示:

<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
    <persistence-unit name="com.groupgti.esb.online.tests">
        <provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
        <class>com.groupgti.esb.assessments.model.jpaimpl.Assessment</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <validation-mode>NONE</validation-mode>
        <properties>
            <property name="openjpa.Log" value="slf4j"/>
            <property name="openjpa.DataCache" value="false"/>
            <property name="openjpa.ReadLockLevel" value="none"/>
            <property name="openjpa.WriteLockLevel" value="pessimistic-write"/>
            <property name="openjpa.LockTimeout" value="10000"/>
            <property name="openjpa.RuntimeUnenhancedClasses" value="unsupported"/>
        </properties>
    </persistence-unit>
</persistence>

整个应用程序使用Spring，并且完成事务的类被标记为@Transactional。 ORM中如何解决这个死锁问题？

编辑:

AssessmentKey 与 Assessment 相关:

@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE}, mappedBy = "assessmentKey")
private List<Assessment> assessments = new ArrayList<Assessment>();

在Assessment中AssessmentKey看起来像这样:

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@Index
@Column(nullable = false)
@ForeignKey
private AssessmentKey assessmentKey;

Answer 1

AssessmentKey 和 Assessment 是 OneToMany 双向关系。OneToMany 和 ManyToOne 都是双向关系> 注释有 CascadeType.PERSIST 等。

要点是:

当EntityManager持续存在Assessment时，AssessmentKey也会持续存在。您应该需要再次保留或合并 AssessmentKey。

让我建议如下 OR 映射:

AssessmentKey.java

@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REMOVE}, 
           mappedBy = "assessmentKey", orphanRemoval=true)
private List<Assessment> assessments;

评估.java

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.REFRESH})
@JoinColumn(name = "ASSESSMENT_ID", referencedColumnName = "ID")
private AssessmentKey assessmentKey;

数据库操作

@Override
public AssessmentKey update(AssessmentKey assessmentKey) {
    OpenJPAEntityManager openJpaEntityMgr = OpenJPAPersistence.cast(entityManager);
    // there may be your operation
    return entityManager.merge(assessmentKey);
}

我假设，当前AssessmentKey对象的Assessment值可能如下

On System                               |   In Existing Database
ID      Description                     |   ID      Descrition
1001    AAA         => No Changes       |   1001    AAA
1002    BBB         => Need to update   |   1002    BB
null    DDD         => Need to add      |   1003    CCC     => need to remove.

当EntityManager合并AssessmentKey时，EntityManager将完​​成Assessment的所有过程，正如我在上面的数据结构中提到的。

注意:确保 OneToMany 注释中的 orphanRemoval=true。