In case anybody finds this thread…

For persist()

The semantics of this method are defined by JSR-220.

persist() is well defined. It makes a transient instance persistent. However, it doesn’t guarantee that the identifier value will be assigned to the persistent instance immediately, the assignment might happen at flush time. The spec doesn’t say that, which is the problem I have with persist().

persist() also guarantees that it will not execute an INSERT statement if it is called outside of transaction boundaries. This is useful in long-running conversations with an extended Session/persistence context.

For save() it says, it is the hibernate standard.

first assigning a generated identifier.

save() does not guarantee the same, it returns an identifier, and if an INSERT has to be executed to get the identifier (e.g. “identity” generator, not “sequence”), this INSERT happens immediately, no matter if you are inside or outside of a transaction. This is not good in a long-running conversation with an extended Session/persistence context.