spring-data-jpa 中的 flush 方法如何工作？

Question

我有使用spring-boot-2.0.3 与spring-data-jpa-2.0.3 和postgresql-9.5.13 的示例项目。它只有三个类：@Entity、@Repository 和主类。 DB 只有一张表，有两个字段：id 和name。

我正在尝试将循环中的INSERT100 000 记录放入表中并测量执行时间 - 为每 100 条记录启用或禁用 EntityManager 类中的 flush() 方法。

预期的结果是启用flush() 方法的执行时间比禁用的要少得多，但实际上我得到了相反的结果。

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问题：我做错了什么？

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项目结构：

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application.properties

spring.datasource.driver-class-name=org.postgresql.Driver
spring.datasource.url=jdbc:postgresql://localhost:5432/twofold
spring.datasource.username=postgres
spring.datasource.password=postgres

---

User.java

package twofold.data;

import javax.persistence.*;

@Entity
@Table(name = "users", schema = "public")
public class User {

    private Long id;
    private String name;

    public User() {}

    public User(String name) {
        this.name = name;
    }

    @Id
    @SequenceGenerator(name = "users_id_seq", sequenceName = "users_id_seq", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "users_id_seq")
    @Column(name = "id", nullable = false)
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Column(name = "name", nullable = false, length = 50)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "id: " + id + "; name: " + name + ";";
    }
}

---

UserRepository.java

package twofold.data;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
}

---

Application.java

package twofold;

import twofold.data.User;
import twofold.data.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.transaction.annotation.Transactional;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Autowired
    private UserRepository userRepository;

    @PersistenceContext
    private EntityManager entityManager;

    @Bean
    public CommandLineRunner addUsers() {
        return new CommandLineRunner() {
            @Transactional
            public void run(String... args) throws Exception {
                long incoming = System.currentTimeMillis();
                for (int i = 1; i <= 100000; i++) {
                    userRepository.save(new User(i + "_name"));
                    if (i % 100 == 0) {
                        entityManager.flush();
                        entityManager.clear();
                    }
                }
                System.out.println("Time: " + (System.currentTimeMillis()-incoming));
            }
        };
    }
}

Answer 1

您必须设置以下休眠属性。

<property name="hibernate.jdbc.batch_size" value="25" />
<property name="hibernate.order_inserts" value="true" />
<property name="hibernate.order_updates" value="true" />

然后这样做：

int entityCount = 50;
int batchSize = 25;

EntityManager entityManager = entityManagerFactory().createEntityManager();
EntityTransaction entityTransaction = entityManager.getTransaction();

try {
    entityTransaction.begin();
    for (int i = 0; i < entityCount; i++) {
        if (i > 0 && i % batchSize == 0) {
            entityTransaction.commit();
            entityTransaction.begin();

            entityManager.clear();
        }
        Post post = new Post(
                String.format("Post %d", i + 1)
        );
        entityManager.persist(post);
    }
    entityTransaction.commit();
} catch (RuntimeException e) {
    if (entityTransaction.isActive()) {
        entityTransaction.rollback();
    }
    throw e;
} finally {
    entityManager.close();
}