Hi Timour, Found another possible issue: The code in best_extension_by_limited_search() calls join->static_pushdown_cost(). static_pushdown_cost() may modify join->position[$I].read_time for any $I. Now, consider an example: SELECT * FROM t1,t2,t3 WHERE subquery_conditions The join optimizer will consider join orders: S1: t1 S2: t1 t2 S3: t1 t2 t3 S4: t1 t3 t2 On step S3, we will get a complete join order, and the new code in best_extension_by_limited_search() is invoked. It will call join->static_pushdown_cost(...) which may change the value of join->position[0].read_time On step S4, we again will get a complete join order. The new code in best_extension_by_limited_search() is invoked, it will call join->static_pushdown_cost(...), which again may change join->position[0].read_time Now, that value will be meaningless. BR Sergei -- Sergei Petrunia, Software Developer MariaDB | Skype: sergefp | Blog: http://s.petrunia.net/blog