5.6. Transactional Behavior with JBoss Data Source Types JBoss Enterprise Application Platform allows creation of different types of data sources, based on their transactional capabilities. The type of data source you create for your VDB's sources also dictates if that data source will be participating the distributed transaction or not, irrespective of the transaction scope you selected from above. Here are different types of data sources: xa-datasource: Capable of participating in the distributed transaction using XA. This is the recommended type be used with any JBoss Data Virtualization sources. local-datasource: Does not participate in XA, unless this is the only local-datasource participating among other xa-datasources in the current distributed transaction. This technique is called last commit optimization. However, if you have more than one local datasource participating in a transaction, the transaction manager will throw an exception: "Could not enlist in transaction on entering meta-aware object!" . no-tx-datasource: Does not participate in distributed transaction at all. In the scope of a JBoss Data Virtualization command over multiple sources, you can include this type of datasource in the same distributed transaction context, however this source will not be subject to any transactional participation. Any changes done on this source as part of the transaction scope, cannot be rolled back. For example, if you have three different sources A, B, C being used in JBoss Data Virtualization, here are some variations on how they behave with different types of data sources. The suffixes "xa", "local", "no-tx" define different type of sources used. A-xa B-xa, C-xa : Can participate in all transactional scopes. No restrictions. A-xa, B-xa, c-local: Can participate in all transactional scopes. Note that there is only one single source, "local". It is assumed that, in the Global scope, any third party datasource other than JBoss Data Virtualization datasource is also XA. A-xa, B-xa, C-no-tx : Can participate in all transactional scopes. Note "C" is not bound by any transactional contract. A and B are the only participants in the XA transaction. A-xa, B-local, C-no-tx : Can participate in all transactional scopes. Note "C" is not bound by any transactional contract, and there is only a single "local" source. If any two or more sources are "local" : They can only participate in Command mode with "autoCommitTxn=OFF". Otherwise they will end with an exception and the message "Could not enlist in transaction on entering meta-aware object!;" because it is not possible to do a XA transaction with "local" datasources. A-no-tx, B-no-tx, C-no-tx : Can participate in all transaction scopes, but none of the sources will be bound by transactional terms. This is equivalent to not using transactions or setting Command mode with "autoCommitTxn=OFF". Important Teiid Designer creates a "local" data source by default. This is not optimal for XA transactions. To create XA datasources, use the Management Console. You can find examples in the EAP_HOME /docs/teiid/datasources directory. If your datasource is not XA, and not the only local source and cannot use "no-tx", then you can look into extending the source to implement the compensating XA implementation. Define your own resource manager for your source and manage the transaction the way you want it to behave. Note that this could be complicated if your source natively does not support the distributed XA protocol. In summary: Use XA datasource if possible Use no-tx datasource if applicable Use autoCommitTxn = OFF, and let go distributed transactions, though not recommended Write a compensating XA based implementation. Table 5.4. Data Virtualization Transaction Participation Teiid-Tx-Scope XA source Local Source No-Tx Source Local always Only If Single Source never Global always Only If Single Source never Auto-commit=true, AutoCommitTxn=ON always Only If Single Source never Auto-commit=true, AutoCommitTxn=OFF never never never Auto-commit=true, AutoCommitTxn=DETECT always Only If Single Source never

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