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From "Patrick Linskey (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 00:34:32 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12486819
] 

Patrick Linskey commented on OPENJPA-182:
-----------------------------------------

In the hint-based approach, you could set the hints on a particular query.

In my approach, you could configure the FetchPlan for a particular query (get the Query's
fetch plan), or for a particular entity manager (get the EM's fetch plan). To do different
fetch plans for different queries, you'd just set the different query fetch plans differently.

Query fetch plans are a copy-on-write semantic -- they start off just delegating through to
the EM's fetch plan, and if you make changes, then they immediately make a copy of the EM's
fetch plan, and remain isolated from the EM's fetch plan from then on out.

If you wanted to do different isolation levels for different find() calls or different relationship
traversals, in my impl, you'd need to set the EM's fetch plan, do the work, then set it back.
In the hint-based impl, you would not be able to do any configuration for find() or relationship
traversals.

> 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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