Spring数据JPA本机查询跳过锁定

Question

我想使用Spring Data JPA在Oracle上执行SKIP LOCKED查询，所以我尝试了以下方法：

@Lock(LockModeType.PESSIMISTIC_WRITE)
@Query(value = "SELECT * FROM User WHERE ID=?1 FOR UPDATE SKIP LOCKED", nativeQuery = true)
User findOne(UUID id);

我尝试了上面的内容，发现生成的查询包含FOR UPDATE，但不包含SKIP LOCKED（下面是从日志生成的查询）：

select ent0_.column1 as name, ent0_.CREATED_DATE as CREATED_2_33_0_ from TABLE_NAME alias_name where ent0_.column1=? for update

如果我从查询方法中删除@Lock，生成的查询甚至没有FOR UPDATE。

请根据需要建议如何使用FOR UPDATE SKIP LOCKED生成查询。

Answer 1

加：

@QueryHints（{@ QueryHint（name =“javax.persistence.lock.timeout”，value =“ - 2”）}）

Answer 2

您可以将-2指定为超时值，以便尽可能使用“skip locked”。

PESSIMISTIC_WRITE，javax.persistence.lock.timeout设置为-2

UPGRADE_SKIPLOCKED

锁获取请求会跳过已锁定的行。它在Oracle和PostgreSQL 9.5中使用SELECT ... FOR UPDATE SKIP，或在SQL Server中使用SELECT ... with（rowlock，updlock，readpast）。

public interface MyRepository extends CrudRepository<MyEntity, Long> {

    /**
     * The lock acquisition request skips the already locked rows.
     * It uses a SELECT …​ FOR UPDATE SKIP LOCKED in Oracle and PostgreSQL 9.5,
     * or SELECT …​ with (rowlock, updlock, readpast) in SQL Server.
     */
    String UPGRADE_SKIPLOCKED = "-2";

    @Lock(value = LockModeType.PESSIMISTIC_WRITE) // adds 'FOR UPDATE' statement
    @QueryHints({@QueryHint(name = "javax.persistence.lock.timeout", value = UPGRADE_SKIPLOCKED)})
    MyEntity findFirstByStatus(String status);

}

通过这样做，选择查询将具有select ... for update skip locked

https://docs.jboss.org/hibernate/orm/5.0/userguide/html_single/chapters/locking/Locking.html