Last Resource Commit optimization for JDBC
There is one caveat with Last Resource Commit. There is a small chance that a transaction ends up with inconsistent results across participating resources if BTM crashes while a transaction is in-flight. The chance is small but it exists so be careful when using that feature. This is in no way a limitation of BTM but of the concept itself.
Please note that if you only intend to run transactions against a single database using Last Resource Commit this scenario is 100% safe, otherwise not.
In theory, only databases supporting XA and providing a
javax.sql.XADataSource implementation can be used with transaction managers. In practice, there is a way around this limitation.
The Last Resource Commit optimization (sometimes referred to as Last Resource Gambit or Last Agent optimization) allows a single non-XA database to participate in a XA transaction by cleverly ordering the resources.
There can be at most one datasource emulating XA with Last Resource Commit participating in a transaction. If it happens that you're trying to use a second emulating datasource while one has already been used, BTM will throw an exception. Again, this is not a limitation of BTM but of the concept itself.
To enable it, you just have to create a
PoolingDataSource using the bitronix.tm.resource.jdbc.lrc.LrcXADataSource as the
Here's an example of code configuring a HSQLDB datasource:
PoolingDataSource myDataSource = new PoolingDataSource(); myDataSource.setClassName("bitronix.tm.resource.jdbc.lrc.LrcXADataSource"); myDataSource.setUniqueName("hsqldb"); myDataSource.setMaxPoolSize(5); myDataSource.setAllowLocalTransactions(true); myDataSource.getDriverProperties().setProperty("driverClassName", "org.hsqldb.jdbcDriver"); myDataSource.getDriverProperties().setProperty("url", "jdbc:hsqldb:/the/db/path"); myDataSource.getDriverProperties().setProperty("user", "sa"); myDataSource.getDriverProperties().setProperty("password", "theSaPassword");
and the same example viewed as a Resource Loader configuration
resource.ds.className=bitronix.tm.resource.jdbc.lrc.LrcXADataSource resource.ds.uniqueName=hsqldb resource.ds.maxPoolSize=5 resource.ds.allowLocalTransactions=true resource.ds.driverProperties.driverClassName=org.hsqldb.jdbcDriver resource.ds.driverProperties.url=jdbc:hsqldb:/the/db/path resource.ds.driverProperties.user=sa resource.ds.driverProperties.password=theSaPassword
The LRC implementation relies on the
BTM 1.3.1 and higher are immune to this problem as these settings are enforced when