Commits this transaction.

def commit(self):
        """
        Commits this transaction.
        """
        self._check_thread()
        if self.state != _STATE_ACTIVE:
            raise TransactionError("Transaction is not active.")
        try:
            self._check_timeout()
            request = transaction_commit_codec.encode_request(self.id, self.thread_id)
            self.client.invoker.invoke_on_connection(request, self.connection).result()
            self.state = _STATE_COMMITTED
        except:
            self.state = _STATE_PARTIAL_COMMIT
            raise
        finally:
            self._locals.transaction_exists = False