jpa 처음 공부하는 학생입니다 ㅠ복습하다가 질문드립니다!

package hellojpa;

import javax.persistence.*;

public class JpaMain {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");

        EntityManager em =emf.createEntityManager();

        EntityTransaction tx = em.getTransaction();
        tx.begin();
        try {
//      Member member1 = new Member();
//      member1.setName("gggg");
//      Member member2 = new Member();
//      member1.setName("gggg2");
//      em.persist(member1);
//      em.persist(member2);     <-이렇게 하면
//Hibernate:
//    call next value for hibernate_sequence
//Hibernate:
//    call next value for hibernate_sequence 이렇게 나오고 insert문이 안나오고
//                                           데이타베이스에 커밋이 안되구요
            Member member1 = new Member();
            member1.setName("gggg");
            Member member2 = new Member();
            em.persist(member1);    //<-이렇게 하면 insert문도 정상적으로 나오는데 차이점을 모르겠어요 ㅠㅠ


            tx.commit();
        }catch (Exception e) {
            tx.rollback();
        }finally {
            em.close();;
        }
        emf.close();
    }
}

package hellojpa;

import javax.persistence.*;
import java.util.Date;

@Entity
public class Member {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "ID")
    private Long id;
    @Column(name = "NAME",nullable = false,length = 10)
    private String name;
    private Integer age;
    @Enumerated(EnumType.STRING)
    private RoleType roleType;
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdDate;
    @Temporal(TemporalType.TIMESTAMP)
    private Date lastModifedDate;
    @Lob
    private String description;

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public RoleType getRoleType() {
        return roleType;
    }

    public void setRoleType(RoleType roleType) {
        this.roleType = roleType;
    }

    public Date getCreatedDate() {
        return createdDate;
    }

    public void setCreatedDate(Date createdDate) {
        this.createdDate = createdDate;
    }

    public Date getLastModifedDate() {
        return lastModifedDate;
    }

    public void setLastModifedDate(Date lastModifedDate) {
        this.lastModifedDate = lastModifedDate;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}