Someone adds Transactional to a method and it does not seem to work. What are the usual reasons?

The annotation is implemented with a proxy, so it only applies when the call comes through the bean from outside. A call from another method inside the same class bypasses the proxy entirely, which is the most common cause. Other reasons: the method is not public, the exception thrown is checked so it does not trigger a rollback by default, the bean was created outside the container, or a new transaction was needed and the propagation was left as required.

Nine times out of ten it is self invocation. Spring wraps the bean in a proxy, and the transaction starts when a caller goes through that proxy, so if a public method in the same class calls the annotated method directly, the call never leaves the object and no transaction begins. The fix is to move the method to another bean or inject the bean into itself, and the honest fix is usually that the boundary was in the wrong place anyway. After that I check the basics: the method should be public, the bean must be Spring managed rather than created with new, and the rollback rule catches people out because by default it only rolls back on unchecked exceptions, so a checked exception commits unless I specify rollbackFor. I also look for propagation, since work that must survive the caller's rollback needs requires new, and that takes a second connection, which matters if the pool is small. And I keep transactions short: no HTTP calls, no message publishing, no waiting on anything inside one, because holding a database connection while calling a third party is how a pool gets exhausted.