@Entity
@Getter
@Setter
public class A {

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  private Long id;

  private String name;

  @OneToMany(mappedBy = "a", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
  List<B> bList;


}

create table A(
  id bigint DEFAULT nextval('a_id_seq') primary key ,
  name text
);

@Entity
@Getter
@Setter
public class B {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private String name;

  @ManyToOne
  @JoinColumn(name="a_id", nullable=false)
  private A a;
}

create table B(
  id bigint generated always as identity primary key,
  name text,
  a_id bigint references a on delete cascade

)

  @PutMapping
  public String updateAllTest(){
    var list=bRepository.findAll();
    for (int i = 0; i <list.size() ; i++) {
      list.get(i).setName("bbb"+i);

    }
    bRepository.saveAll(list);
    return "OK";
  }

    23500 nanoseconds spent acquiring 1 JDBC connections;
    0 nanoseconds spent releasing 0 JDBC connections;
    16052000 nanoseconds spent preparing 2501 JDBC statements;
    9248371100 nanoseconds spent executing 2500 JDBC statements;
    10362668600 nanoseconds spent executing 5 JDBC batches;
    0 nanoseconds spent performing 0 L2C puts;
    0 nanoseconds spent performing 0 L2C hits;
    0 nanoseconds spent performing 0 L2C misses;
    10398905100 nanoseconds spent executing 1 flushes (flushing a total of 2500 entities and 0 collections);
    0 nanoseconds spent executing 0 partial-flushes (flushing a total of 0 entities and 0 collections)

  27300 nanoseconds spent acquiring 1 JDBC connections;
    0 nanoseconds spent releasing 0 JDBC connections;
    3439100 nanoseconds spent preparing 101 JDBC statements;
    401003800 nanoseconds spent executing 100 JDBC statements;
    391480100 nanoseconds spent executing 1 JDBC batches;

    select
        b0_.id as id1_11_0_,
        b0_.a_id as a_id2_11_0_,
        b0_.name as name3_11_0_ 
    from
        b b0_ 
    where
        b0_.id=?

   update
        b 
    set
        a_id=?,
        name=? 
    where
        id=?