内存相关变量
these server variables control the amount of memory allocated to the various buffers and caches within mysql.
以下这些服务器变量控制这mysql分配给各种缓冲或者换缓存的内存总数。
join_buffer_size
(per session) controls the amount of memory allocated to perform joins on tables that have no keys which can be used to perform a condition filter. allocated for each table joined without necessary filter conditions
(会话变量) 控制在对没有索引的表连接时分配的内存总数，它可以用做条件过滤器。为连接中的每个表分配而无需必要的过滤条件。
key_buffer_size
(global) (myisam-only) controls the amount of memory allocated to the myisam index key cache
(全局变量) (只针对myisam表) 空置分配给myisam索引缓存的内存总数。
innodb_buffer_pool_size
(global) (innodb-only) controls the amount of memory allocated to the innodb cache containing both clustered data and secondary index pages
(全局变量) (只针对innodb) 控制分配给包括集群数据以及次要索引页的innodb缓存的内存总数。
innodb_additional_mem_pool_size
(global) (innodb-only) controls the amount of memory allocated to the buffer storing the innodb internal data dictionary
(全局变量) (只针对innodb) 控制分配给对innodb内部数据字典进行排序所需的缓冲。
innodb_log_buffer_size
(global) (innodb-only) controls the amount of memory allocated to the buffer storing innodb write-ahead log entries
(全局变量) (只针对innodb) 控制分配给对innodb存储提前写日志记录所需的缓冲。
query_cache_size
(global) controls the amount of memory allocated to the query cache
(全局变量) 控制分配给查询缓存的内存总量。
read_buffer_size
(per session) controls the amount of memory allocated to the connecting thread in order to process a table scan
(会话变量) 控制分配给处理扫描表的连接线程内存总数。
read_rnd_buffer_size
(per session) controls the amount of memory allocated to the buffer used to read previously sorted results
(会话变量) 控制分配给读取当前排序完的结果所需的缓冲总数。
sort_buffer_size
(per session) controls the amount memory allocated to the buffer used to sort result sets before returning the set to the calling client
(会话变量) 控制在把结果返回给调用的客户端之前需要对结果集进行排序所需的缓冲总数。
thread_stack
(per session) controls the default stack memory allocated for each connecting thread
(会话变量) 控制分配给每个连接线程的默认堆栈内存总数。
tmp_table_size
(global) controls the maximum memory to allocate to a temporary table before mysql converts it into an on-disk myisam table
(全局变量) 控制mysql在把一个临时表转换成磁盘存储的myisam表时所需的最大内存总数。
thread-related variables
线程相关变量
thread_cache_size
(global) determines the number of thread connection objects that mysql keeps in a cache to mitigate resource creation costs
(全局变量) 确定mysql在缓存中保持的连接线程数量，这能减少创建连接时所需的系统资源