活动链接（动态）使用的内存数量如下所示：
per_connection_memory = read_buffer_size //memory for sequential table scans +read_rnd_buffer_size // memory for buffering reads +sort_buffer_size // memory ofr in mem sorts +thread_stack //per connection memory +join_buffer_size // memory for in mem table joins
每台服务器（固定）使用内存的数量如下所示：
per_server_memory = tmp_table_size //memory for all temp tables +max_heap_table_size // max size of single temp table +key_buffer_size //memory allocated for index blocks +innodb_buffer_pool_size // main cache for InnoDB data +innodb_additional_mem_pool_size // InnoDB record structure cache +innodb_log_buffer_size // log file write buffer +query_cache_size // compiled statement cache
Mysql可以使用的最大内存定义如下：
max_memory = (per_connection_memory* max _connections) + per_server_memory
原文：http://www.cnblogs.com/martinjinyu/p/4711745.html