查询JOIN FETCH性能问题 [英] Query with JOIN FETCH performance problem

问题描述

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：

I have problem with hibernate query performance which I can't figure out. In code snippet below I need select entities with at least one mapping and filtered mapping. I'm using FETCH JOIN for this to load only filtered mappings. But in that case I have performance problems with query. Hibernate says warning log :

org.hibernate.hql.ast.QueryTranslatorImpl
- 使用collection fetch指定的firstResult / maxResults;申请
内存！

org.hibernate.hql.ast.QueryTranslatorImpl - firstResult/maxResults specified with collection fetch; applying in memory!

当我省略FETCH JOIN并且只留下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。

When I omit FETCH JOIN and left only JOIN query is nice fast. But in result I have all mappings loaded to entity which is not acceptable state for me. Is there a way to boost query performance? There are a lot rows in mapping table.

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

推荐答案

增加JVM的内存后，情况要好得多。毕竟我在查询中没有使用FETCH结束。

after increasing memory for JVM things goes much better. After all I end with not using FETCH in queries.

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