java - Hibernate二级缓存并不是在所有情况下都使用

Question

使用 Spring Boot 2、Spring Data JPA 和 Hibernate。我正在尝试对一些从未更新的实体使用 Hibernate 的二级缓存。

在我的例子中，实体DocumentType与其他实体相关，因此当查询一种文档类型时，Hibernate 会进行 4 个 sql 查询。 当使用Hibernate二级缓存时，缓存用于某些实体，但仍然有一个sql查询到数据库。 我想了解为什么在一种情况下不使用缓存。

这就是我的实体的样子:

@Entity
@Table(name = "document_type")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class DocumentType {

    @Id
    private Long id;

    @Column
    private String subtypeCode;

    @OneToOne(cascade = {CascadeType.ALL})
    private Translation translation;

    @org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "business", joinColumns = @JoinColumn(name = "document_type_id"))
    @Enumerated(EnumType.STRING)
    @Column(name = "business")
    private Set<Business> businesses;

    @ManyToOne(cascade = {CascadeType.ALL})
    @JoinColumn(name = "equivalence_id")
    private Equivalence equivalence;

@Entity
@Table(name = "equivalence")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class Equivalence {

    @Id
    private Long id;

    @org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
    @OneToMany(mappedBy="equivalence", fetch = FetchType.EAGER)
    private List<DocumentType> documentTypeList;

当我第一次使用此方法获取文档类型时:

@Repository
public interface DocumentTypeRepository extends JpaRepository<DocumentType, Long> {

    DocumentType findBySubtypeCode(String subtypeCode);

我有以下 session 指标:

    1704919 nanoseconds spent preparing 4 JDBC statements;
    33284024 nanoseconds spent executing 4 JDBC statements;
    0 nanoseconds spent executing 0 JDBC batches;
    2983589 nanoseconds spent performing 4 L2C puts;
    0 nanoseconds spent performing 0 L2C hits;
    1313315 nanoseconds spent performing 3 L2C misses;

第二次获取相同的文档类型会给出:

    27855 nanoseconds spent preparing 1 JDBC statements;
    4348289 nanoseconds spent executing 1 JDBC statements;
    0 nanoseconds spent executing 0 JDBC batches;
    14421 nanoseconds spent performing 1 L2C puts;
    182655 nanoseconds spent performing 3 L2C hits;
    0 nanoseconds spent performing 0 L2C misses;

我希望第二次有 0 条 JDBC 语句，但事实并非如此。

Answer 1

二级缓存仅在通过 ID 检索实体时才起作用，可以使用 EntityManager.find(...)或者当 JPA 需要获取相关实体时在内部。默认情况下，查询结果不会被缓存。

你想要的是Hibernate query cache和 org.hibernate.cacheable查询提示。或者，您可以启用 Spring 缓存并使用 @Cacheable或@CachePut注解。