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javaoracle-databasejpalockingeclipselink

Select for update skip locked from JPA level

In my application - Oracle with JPA (EclipseLink), I'm using the following expression to lock the subset of the records in some tables:

select * from MY_TABLE where MY_CONDITIONS for update skip locked

I run it throughout native query, but I have to write that query for all required entities.

Is there any way to skip locked records using pure JPA? Can I implement my own locking policy?

I don't mind changing JPA provider but I want to use JPA API.

Solution

  • Hibernate provides the UPGRADE_SKIPLOCKED Lock mode.

    Using JPA and Hibernate, to produce a "SKIP_LOCKED" as per Hibernate LockMode documentation, you have to combine the PESSIMISTIC_WRITE JPA LockModeType:

    entityManager.find(Department.class, 1, LockModeType.PESSIMISTIC_WRITE);

    and the Lock timeout setting, like for example in persistence.xml for your persistence unit:

    <properties>
   <property name="javax.persistence.query.timeout" value="-2"/>
</properties>

    (Note that you can configure this LockMode for complex query as well)

    SKIP LOCKED is not part of ANSI SQL. Some RDBMS such the following provide this as a specific feature:

    So with pure JPA, it is not possible to specify a "SKIP LOCKED" in queries. Indeed, as documented in LockModeType, JPA 2.1 only supports the following:

    • NONE
    • OPTIMISTIC
    • OPTIMISTIC_FORCE_INCREMENT
    • PESSIMISTIC_FORCE_INCREMENT
    • PESSIMISTIC_READ
    • PESSIMISTIC_WRITE
    • READ
    • WRITE

    However, to enable SKIP LOCKED in your query you can use these alternatives:

    • Use specific JPA implementation feature, such as Hibernate LockMode which allows to specify the SKIP LOCKED via a JPA query, thanks to a combination of PESSIMISTIC_WRITE LockModeType Lock Timeout specific setting as described above
    • Create a native SQL query as you did