查询JOIN FETCH性能问题

Question

我有hibernate查询性能的问题,我无法弄清楚.在下面的代码片段中,我需要选择具有至少一个映射和过滤映射的实体.我正在使用FETCH JOIN来加载仅过滤的映射.但在这种情况下,我的查询存在性能问题.Hibernate说警告日志:

org.hibernate.hql.ast.QueryTranslatorImpl - 使用collection fetch指定的firstResult/maxResults; 在记忆中应用!

当我省略FETCH JOIN并且只剩下JOIN查询时很快.但结果我将所有映射加载到实体,这对我来说是不可接受的状态.有没有办法提高查询性能？映射表中有很多行.

HQL查询:

select distinct e from Entity 
   join fetch e.mappings as mapping 
where e.deleted = 0 and e.mappings is not empty 
   and e = mapping.e and mapping.approval in (:approvals)

实体:

@Entity
@Table(name="entity")
class Entity {

   ...

   @OneToMany(mappedBy="entity", cascade=CascadeType.REMOVE, fetch=FetchType.LAZY)
   @OrderBy("created")
   private List<Mapping> mappings = new ArrayList<Mapping>();

   ...
}

@Entity
@Table(name="mapping")
class Mapping {

public static enum MappingApproval {
    WAITING, // mapping is waiting for approval
    APPROVED, // mapping was approved
    DECLINED; // mapping was declined
}

...

    @ManyToOne(fetch=FetchType.EAGER)
    @JoinColumn(name="entity_id", nullable=false)
    private Entity entity;

    @Enumerated(EnumType.STRING)
    @Column(name="approval", length=20)
    private MappingApproval approval;

...

}

谢谢

Answer 1

增加 JVM 内存后，情况好多了。毕竟我最终没有在查询中使用 FETCH。