It appears it's not possible to restore to an savepoint within in a XA transaction
this gives error:
Error Code: 1399. XAER_RMFAIL: The command cannot be executed when global transaction is in the ACTIVE state
When i try the exact same query in mysql (5.7), this produces no errors, also the transaction is restored to the actual savepoint.
When savepoints wouldn't be supported in XA transactions, i would expect the SAVEPOINT x would already result in an error.