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.
No it is not a typo.It was intended.
On 4/4/07, Patrick Linskey (JIRA) <[EMAIL PROTECTED]> wrote:
[
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.
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