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https://issues.apache.org/jira/browse/OPENJPA-2806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17169844#comment-17169844
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chenlin commented on OPENJPA-2806:
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Entity Locking API：
’OpenJPA differentiates between PESSIMISTIC_READ and PESSIMISTIC_WRITE lock
modes only with DB2 databases. While running with other databases, there is no
distinction between these two modes because PESSIMISTIC_READ lock mode is
upgraded to PESSIMISTIC_WRITE.
In other words, only DB2 can achieve your expectations with PESSIMISTIC_READ. ‘
You are advised to use another method to implement the required functions.
ps：https://openjpa.apache.org/builds/2.2.2/apache-openjpa/docs/jpa_overview_em_locking.html
> PESSIMISTIC_READ takes out exclusive lock on Postgres
> -----------------------------------------------------
>
> Key: OPENJPA-2806
> URL: https://issues.apache.org/jira/browse/OPENJPA-2806
> Project: OpenJPA
> Issue Type: Bug
> Components: kernel
> Affects Versions: 2.4.2, 3.0.0, 3.1.0
> Reporter: Pawel Veselov
> Priority: Major
> Attachments: openjpa-lock.zip
>
>
> I've found out that using PESSIMISTIC_READ on an entity with postgres
> uses 'for update' lock, which is actually exclusive.
> I understand JPA specification says that it's permissible to do that,
> but I really need a shared lock for what I'm trying to achieve.
> Is it possible to control somehow? I've had to resolve to using native
> queries, and I'd like to avoid this as much as possible...
> Attached is a test.
> Change App.java to control database properties for connection (top of
> `main()`)
> Run App.class to execute the test. If the lock taken by OpenJPA is exclusive,
> then native query will fail (with an exception).
> I'm testing on Postgres 9.6
> Tested with 2.4.2, 3.0.0 and 3.1.0
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