Karaf instance can wrongly obtain a lock when the locking table is empty on a
Oracle DB
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Key: KARAF-689
URL: https://issues.apache.org/jira/browse/KARAF-689
Project: Karaf
Issue Type: Bug
Components: runtime
Affects Versions: 2.1.3
Environment: Oracle Database 11g Enterprise Edition Release 11.2.0.2.0
- 64bit Production
Reporter: Ton Swieb
When running Karaf in Master/Slave mode a Karaf instance can wrongly obtain a
lock when the locking table is empty on a Oracle DB.
Karaf creates a lock table and a lock record in de OracleDB upon first usage.
When the lock record is removed afterwards without dropping the table then the
locking mechanisme does not work anymore and any instance can wrongly obtain a
lock.
This is not an issue for other database systems, because the implementation for
other DB systems periodically tries to update the lock record and verify how
many records are updated. According to the documentation in the code the
"update" functionality has been removed for Oracle because it can exhaust the
Oracle UNDO log.
I created a patch which does not use the "update" functionality, but executes
an extra check after we acquired the lock. It checks if the SELECT FOR UPDATE
used for the lock has not been executed on an empty selection, because when the
selection is empty then the locking functionality will not work as expected.
Can you apply this patch to the branches karaf-2.1.x and karaf-2.2.x and the
trunk. I looked at the SVN history of the files I have modified and noticed
that they are the same in both branches and the trunk.
The patch has been created against the karaf-2.1.x branch.
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