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https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487086
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Patrick Linskey commented on OPENJPA-182:
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> > I know that Oracle allows you to add a FOR UPDATE clause
> > to a query, and this affects the results of that query. In Sun
> > appserver CMP we use this to set exclusive locks on rows
> > where we want pessimistic locking behavior just for certain tables.
>
> Again, this is exactly what our existing lock levels and APIs do.
The current patches in this issue encompass two separate bits of functionality:
1. an update-override setting. (In the context of my patch, I'm not convinced
that this is necessary, since I suspect that the code that calls toSelect()
might set the forUpdate boolean based on the values in the
JDBCFetchConfiguration anyways.)
2. an isolation-override setting.
Currently, this patch implements all of this only in the DB2Dictionary. As of
right now, the first feature is something that is useful for all sorts of
databases, via syntax like Oracle's SELECT ... FOR UPDATE. However, we only
know how to implement the second feature for DB2, and not for any other
database. In Oracle, "ALTER SESSION" can be used to change the isolation level
of a given session, but I'm not sure of the semantics of this operation. I
believe that Abe's question is: Do other databases (Sybase? Derby?) also have
semantics for changing the isolation level of a particular query?
> db2 update lock syntax WITH <isolation> USE AND KEEP UPDATE LOCKS
> ------------------------------------------------------------------
>
> Key: OPENJPA-182
> URL: https://issues.apache.org/jira/browse/OPENJPA-182
> Project: OpenJPA
> Issue Type: New Feature
> Components: jdbc
> Environment: db2 database driver for zOS, AS400, Unix, Windows, Linux
> Reporter: David Wisneski
> Assigned To: David Wisneski
> Attachments: OPENJPA-182.patch, openJPA182.patch
>
>
> A while back we changed the syntax of update locking from FOR UPDATE OF to
> WITH RS USE AND KEEP UPDATE LOCKS. Additional changes are required because
> 1. if isolation=serializable is configured, then the syntax should be WITH
> RR USE AND KEEP UDPATE LOCKS
> 2. when using DB2/400 on iSeries machines, the syntax is WITH RS USE AND
> KEEP EXCLUSIVE LOCKS or WITH RR USE AND KEEP EXCLUSIVE LOCKS because DB2/400
> only supports read or exclusive locks.
> 3. DB2 supports both a FETCH FIRST ROWS and update LOCKS clauses.
> So we change supportsLockingWithSelectRange = true in the
> AbstractDB2Dictionary class and change the DB2Dictionary to append the
> correct LOCKS syntax depending on vendor, release and isolation level.
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