Transaction synchronization
is the process by which a persistence context is registered with a transaction so that
the persistence context may be notified when a transaction commits. The provider uses this
notification to ensure that a given persistence context is correctly flushed to the database.

Transaction association
is the act of binding a persistence context to a transaction. You can also
think of this as the active persistence context within the scope of that transaction.

Transaction propagation
is the process of sharing a persistence context between multiple container-managed
entity managers in a single transaction.

persistence context propagation is that the persistence context
propagates as the JTA transaction propagates.

Transaction association for extended persistence contexts is eager.
Likewise in the case of bean-managed
transactions; as soon as UserTransaction.begin() is invoked within a bean method, the container
intercepts the call and performs the same association.

Because a transaction-scoped entity manager will use an existing persistence context
associated with the transaction before it will create a new persistence context, it is possible to
share an extended persistence context with other transaction-scoped entity managers.

only one persistence context could be propagated with a JTA transaction.
the extended persistence context would always try to make itself the active
persistence context.
There can only be one active persistence
context for a transaction.

During the eager association of the
extended persistence context, the container will check to see if there is already an active persistence
context. If there is, it must be the same as the extended persistence context that it is
trying to associate, or an exception will be thrown.

呵呵， 学了不少

While extended persistence context propagation is useful if a stateful session bean with an
extended persistence context is the first EJB to be invoked in a call chain, it limits the situations
in which other components can call into the stateful session bean if they too are using entity
managers.
One way to work around this problem is to change the default transaction attribute for the
stateful session bean that uses the extended persistence context.

QUOTE:

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原帖由 justforregister 于 2008-7-5 18:25 发表
呵呵， 学了不少

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要点，容易混淆和忽视的地方！直接影响设计！

Note that excessive use of the
REQUIRES_NEW transaction attribute can lead to application performance problems as many more
transactions than normal will be created and active transactions will be suspended and resumed.