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From "Craig Russell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-182) db2 update lock syntax WITH <isolation> USE AND KEEP UPDATE LOCKS
Date Thu, 05 Apr 2007 15:09:33 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12486997
] 

Craig Russell commented on OPENJPA-182:
---------------------------------------

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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