Oracle Has introduced new processes in Oracle 11 and above to handle XA type processes.
The Parameter global_txn_processes control is you want GTX processes to spawn or not.
If global_txn_processes >0 oracle will autotune in 11.2.0 the amount of gtx processes it needs per node.
these processes are normally used for distributed transactions and for XA based transactions. if you are using the OracleXA dataclass in your jdbc driver. you are probably using DTP or distributed transaction processing.