How much memory can my MySQL server eat?

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It's based on maximum memory usage of mysql server:

Mysql_max_memory_usage =
       Query_cache_size      +   Key_buffer_size         +
       Myisam_sort_buffer_size   +   Innodb_buffer_pool_size     +
       Innodb_log_buffer_size    +   Innodb_additional_mem_pool_size +
       Max_connections       *
       (
           Sort_buffer_size        +   Read_buffer_size        +
           Read_rnd_buffer_size    +   Join_buffer_size        +
           Thread_stack
       )
Much more info about perfromance you cau get with mysqltuner:
   http://mysqltuner.com/mysqltuner.pl