Hi Zhzhzoo, I see that the current patch uses @@optimizer_trace_enabled variable to control it. Meanwhile, in MySQL the name of the variable is "optimizer_trace". It is a flag set: mysql> select @@optimizer_trace; +-------------------------+ | @@optimizer_trace | +-------------------------+ | enabled=on,one_line=off | +-------------------------+ 1 row in set (0.00 sec) but one can set it to 1 or 0 to just set enabled on/off: mysql> set @@optimizer_trace=1; Query OK, 0 rows affected (0.00 sec) mysql> set @@optimizer_trace=0; Query OK, 0 rows affected (0.00 sec) This obviously carries some legacy but I think we should have it the same way, in order to be compatible with MySQL where possible. Please use the same name/values as MySQL does. BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog