Can not XA COMMIT a recovered prepared XA transaction when autocommit is turned off, this is wrong, the prepared XA txn must be able to be committed regardless of autocommit or other variables except read_only.

MariaDB [test]> xa start 'a'; insert into t1 values(1) ; xa end 'a';xa prepare 'a';
Query OK, 0 rows affected (0.000 sec)

Query OK, 1 row affected (32.514 sec)

Query OK, 0 rows affected (0.000 sec)

Query OK, 0 rows affected (18.742 sec)

MariaDB [test]> quit
Bye
dzw@dzw:~/mysql_installs/mariadb-10.11.4-bin-dbg/bin$ ./mysql -S /tmp/mysql.sock -udzw
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 8
Server version: 10.11.4-MariaDB-debug-log Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> xa recover;
--------------------------------------+

--------------------------------------+

--------------------------------------+
1 row in set (0.000 sec)

MariaDB [(none)]> set autocommit=0;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> xa recover;
--------------------------------------+

--------------------------------------+

--------------------------------------+
1 row in set (0.000 sec)

MariaDB [(none)]> xa commit 'a';
ERROR 1400 (XAE09): XAER_OUTSIDE: Some work is done outside global transaction
MariaDB [(none)]> set autocommit = on;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> xa commit 'a';
Query OK, 0 rows affected (0.006 sec)