Select for update skip locked from JPA level

Question

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.

Answer 1

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:

• MySQL
• Postgresql
• Oracle

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