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https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487046
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Patrick Linskey commented on OPENJPA-182:
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> > Hopefully, this will be useful for applications where there are "hot"
> > tables
> > that require pessimistic locking even though the rest of the application
> > does better with optimistic.
>
> That's what our lock levels and lock APIs are for. I'm still not clear on
> what this is
> adding to the mix for most DBs.
Not really -- the lock levels allow the user to configure how locking should
happen, not what the isolation level should be for the locks.
I don't know about what levels of support non-DB2 databases have for per-query
isolation level configuration. Does anyone have any experience with this in
other databases?
Oh, and regardless, we should change the base DBDictionary to throw an
exception if this FetchPlan setting is set but not serviceable.
One thing that we should test: I'm not convinced that the lock level override
in the DB2Dictionary code is necessary. It's possible that the LockManager will
already take into account the current JDBCFetchConfiguration's lock level
settings when specifying the forUpdate setting for the toSelect() clause. Some
test cases will make it easy to figure out the answer to this question.
> 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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