MariaDB> SELECT GET_LOCK('lock1',10);
        -> 1
MariaDB> SELECT IS_FREE_LOCK('lock2');
        -> 1
MariaDB> SELECT GET_LOCK('lock2',10);
        -> 1
MariaDB> SELECT RELEASE_LOCK('lock2');
        -> 1
MariaDB> SELECT RELEASE_LOCK('lock1');
        -> NULL
