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https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12486997
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Craig Russell 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. Take the example of an Order/OrderLine where there are
lots of updates of the Order and/or associated OrderLine. If several threads
get the same Order, they will ultimately conflict and waste time. If the query
to retrieve the Order is marked as pessimistic (WRITE) then these threads will
serialize and all of their work will complete.
> 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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