As far as I understood DataSourceTransactionManager binds a JDBC connection from the specified DataSource to the current thread, allowing for one thread-bound Connection per DataSource. If it’s a pool of connections, it will take one of the available connections.
After this if I use JdbcTemplate inside a transaction, it will capture a connection binded by DataSourceTransactionManager. Do I understand the mechanism correctly? A there any requirements for making transaction manager bean definition (i.e. singleton)?
You’ve pretty much described how it works. Spring’s transaction synchronization logic has the rather fearsome responsibility for keeping transactions synchronized across JDBC, Hibernate, JPA, etc, and the end result is pretty seamless.
Transaction managers must be singletons, yes. Any one transaction is managed by only one transaction manager, and if you have several of them lying around, you’re in for a world of pain.