[
https://issues.apache.org/jira/browse/OPENJPA-182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Patrick Linskey updated OPENJPA-182:
------------------------------------
Attachment: OPENJPA-182.patch
For the sake of discussion, I've attached an alternate patch that uses a new
JDBCFetchPlan.setIsolationLevel() instead of a hint for isolation level, and
uses JDBCFetchConfiguration.getReadLockLevel() to determine whether or not to
do a SELECT ... FOR UPDATE.
If the read lock level is set to LockLevels.LEVEL_WRITE, then the FOR UPDATE is
included; if the read lock level is set to LockLevels.LEVEL_READ, then no FOR
UPDATE is used. If the read lock level is LockLevels.LEVEL_NONE, then the
default behavior is used. (This is possibly not the best use of LEVEL_NONE --
I'm not sure if LEVEL_NONE means 'default' or something else. But for the
purposes of demonstration, it seemed expedient to use it. Adding a new
LEVEL_DEFAULT constant might make more sense.)
Also, I directly reused the java.sql.Connection constants, which is possibly
non-ideal; we might want to discuss making our own constants. Or not.
So, in this model, if there were a test case for this stuff, I would have
changed the test case to do:
Query q = em.createQuery(...);
JDBCFetchPlan plan = (JDBCFetchPlan) ((OpenJPAQuery) query).getFetchPlan();
plan.setIsolationLevel(Connection.TRANSACTION_SERIALIZABLE);
plan.setReadLockMode(LockModeType.WRITE); // force a FOR UPDATE
List l = q.getResultList();
Note also that this model allows the isolation level and read lock mode to be
configured on the EM itself, for use in find() calls and relationship lookups,
and as the default settings for the fetch plans of queries created from the EM.
Finally, I replicated the logic in DB2Dictionary, but I noticed that sometimes
the logic checked for "serializable" and sometimes it checked for
"read-uncommitted". I preserved these checks, but was this intentional? I'm not
all that clear about what the optimizations are, so just wanted to ensure that
that wasn't a typo.
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
