The JDO specification defines a javax.jdo.Transaction interface that is similar to a JTA transaction. The JDO application will begin a transaction before making changes to objects, and then commit (or rollback) the transaction once the operation is complete. JDO does not mandate any specific transaction demarcation boundries; the application is free to begin and end transactions in the way that the developer deems suitable. See Chapter 9, Transaction.

Not necessarily. For optimistic JDO transactions, Kodo will typically only begin a database transaction when the JDO transaction is committed, or if changes are manually flushed to the database. For pessimistic transactions, Kodo will begin a database transaction only once the first objects are acquired and locked.